Manabu Oguma

Universal linear optics

Complex quantum optical circuitry Encoding and manipulating information in the states of single photons provides a potential platform for quantum computing and communication. Carolan et al. developed a reconfigurable integrated waveguide device fabricated in a glass chip (see the Perspective by Rohde and Dowling). The device allowed for universal linear optics transformations on six wave-guides using 15 integrated Mach-Zehnder interferometers, each of which was individually programmable. Functional performance in a number of applications in optics and quantum optics demonstrates the versatility of the devices reprogrammable architecture. Science, this issue p. 711; see also p. 696 A reconfigurable optical circuit provides a platform for a photonically-based quantum computer. [Also see Perspective by Rohde and Dowling] Linear optics underpins fundamental tests of quantum mechanics and quantum technologies. We demonstrate a single reprogrammable optical circuit that is sufficient to implement all possible linear optical protocols up to the size of that circuit. Our six-mode universal system consists of a cascade of 15 Mach-Zehnder interferometers with 30 thermo-optic phase shifters integrated into a single photonic chip that is electrically and optically interfaced for arbitrary setting of all phase shifters, input of up to six photons, and their measurement with a 12-single-photon detector system. We programmed this system to implement heralded quantum logic and entangling gates, boson sampling with verification tests, and six-dimensional complex Hadamards. We implemented 100 Haar random unitaries with an average fidelity of 0.999 ± 0.001. Our system can be rapidly reprogrammed to implement these and any other linear optical protocol, pointing the way to applications across fundamental science and quantum technologies.

Optical amplification in Er3+‐doped P2O5–SiO2 planar waveguides

The small signal gain of Er3+‐doped P2O5–SiO2 planar waveguides is described with a homogeneous upconversion model. The homogeneous upconversion process accurately describes the absorption saturation at a wavelength of 0.98 μm. Interpretation of the absorption saturation provides homogeneous upconversion coefficients of 4×10−15 cm3 s−1 for a 0.54 wt % Er3+‐doped 14.6 wt % P2O5 codoped silica waveguide and 6×10−18 cm3 s−1 for a 0.46 wt % Er3+‐doped 21.6 wt % P2O5 codoped silica waveguide. The upconversion process occurs in the Er3+ ion rich phase in the P2O5–SiO2 core glass. A calculation that includes the homogeneous upconversion process proves that the gain can be enhanced by codoping the planar waveguide with P2O5. A gain of 20 dB is calculated with an Er3+ ion concentration of 0.4–0.7 wt % and a waveguide length of 40 cm when the pump power is 100 mW and 20 wt % P2O5 codoped Er3+‐doped silica‐based planar waveguides are used.

Dense SDM (12-Core

We propose long-haul space-division-multiplexing (SDM) transmission systems employing parallel multiple-input multiple-output (MIMO) frequency-domain equalization (FDE) and transmission fiber with low differential mode delay (DMD). We first discuss the advantages of parallel MIMO FDE technique in long-haul SDM transmission systems in terms of the computational complexity, and then, compare the complexity required for parallel MIMO FDE as well as the conventional time-domain equalization techniques. Proposed parallel MIMO FDE that employs low baud rate multicarrier signal transmission with a receiver-side FDE enables us to compensate for 33.2-ns DMD with considerably low-computational complexity. Next, we describe in detail the newly developed fiber and devices we used in the conducted experiments. A graded-index (GI) multicore few-mode fiber (MC-FMF) suppressed the accumulation of DMD as well as intercore crosstalk. Mode dependent loss/gain effect was also mitigated by employing both a ring-core FM erbium-doped fiber amplifier and a free-space optics type gain equalizer. By combining these advanced techniques together, we finally demonstrate 12-core × 3-mode dense SDM transmission over 527-km GI MC-FMF without optical DMD management.

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We successfully fabricated a high channel count and flat-top wavelength-division-multiplexing filter by integrating a waveguide-type interleave filter and two arrayed-waveguide grating on one chip. Optimizing the loss ripple of the interleave filter, we realized a 50-GHz spacing, 102-channel ports, a 1-dB passband of 30 GHz, and an insertion loss of 4 dB.

3-Mode) Transmission Over 527 km With 33.2-ns Mode-Dispersion Employing Low-Complexity Parallel MIMO Frequency-Domain Equalization

This paper describes a compact and practical interleave filter with uniform multi/demultiplexing properties and a wide operational wavelength range realized by using a lattice-form structure and a silica-based waveguide. In the design, we optimized the bandwidth by controlling the lattice stage number and the loss ripple in the spectrum. Moreover, we propose a novel coupler with a large fabrication tolerance, a new tandem configuration that provides uniform characteristics and low dispersion, a polarization dependence compensation method, and a folded configuration, which are effective in realizing a high-performance interleave filter. Based on the above techniques, we fabricated a 50-GHz channel spacing interleave filter by using planar-lightwave-circuit technologies and demonstrated that it performed well throughout the C-band, exhibiting a low insertion loss of about 2 dB, a low chromatic dispersion of within +/-20 ps/nm, a 1-dB passband width of over 34 GHz, and a 30-dB stopband width of over 25 GHz, which are sufficient for a 10-Gbps transmission system.

Passband-width broadening design for WDM filter with lattice-form interleave filter and arrayed-waveguide gratings

A low loss wavelength-selective switch is proposed and demonstrated. The switch has a 1/spl times/4 transversal filter configuration that includes arrayed waveguide gratings and thermooptic phase shifters, and can route arbitrary wavelength input light to arbitrary outputs with no loss variation. We confirmed its operating principle and obtained an average loss of 2.7 dB and a worst extinction ratio of more than 20 dB.

Compact and low-loss interleave filter employing lattice-form structure and silica-based waveguide

We present a novel optical OFDM demultiplexer with a silica-PLC-based optical DFT circuit. This compact device can process an arbitrary number of subcarriers. The operation of a ten-channel device is demonstrated by demultiplexing a 100-Gbit/s (10-subcarrier × 10-Gbit/s) OFDM signal.

Low loss fully reconfigurable wavelength-selective optical 1/spl times/N switch based on transversal filter configuration using silica-based planar lightwave circuit

We propose an integrated-photonic device for demultiplexing optical OFDM signals that consists of an optical FFT circuit. An optical demultiplexer for four OFDM sub-carriers is realized, and used to demultiplex 4 times 10 Gbit/s signals.

Integrated-optic OFDM demultiplexer using slab star coupler based optical DFT circuit

We demonstrate an optical orthogonal frequency division multiplexing (OFDM) demultiplexer with an optical discrete Fourier transform circuit fabricated using silica planar lightwave circuit technology. This compact device can process an arbitrary number of subcarriers. The operation of a ten-channel device is demonstrated by demultiplexing a 100 Gbit/s (10 subcarrier × 10 Gbits/s) OFDM signal. We also discuss a main factor affecting characteristics degradation of the device.

Optical OFDM demultiplexer using silica PLC based optical FFT circuit

An integrated-optic device for demultiplexing optical orthogonal frequency-division-multiplexed signals is described that consists of an optical fast-Fourier-transform circuit and optical gates. The fast-Fourier-transform circuit is composed of symmetrical Mach-Zehnder interferometers that are suitable for precisely adjusting filter characteristics. This device can process four or more channels with a relatively simple configuration and reduced size. An optical demultiplexer for four subcarrier channels is realized and used to demultiplex 4 x 10 Gbit/s signals.