Low-loss partial rib polarization rotator consisting only of silicon core and silica cladding.

We present a low-loss and small-footprint polarization rotator based on mode evolution. The polarization rotator is composed of an asymmetric-rib waveguide and a tapered waveguide, both of which consist only of a silicon core and a silica cladding. The rotator is fabricated under the same design rules as other device blocks, such as rib-waveguide phase shifters for photonic integration. The polarization rotator is fabricated using CMOS-based processes and provides polarization rotations with an on-chip insertion loss lower than 0.5 dB from transverse-electric (TE) to transverse-magnetic (TM) polarization and a loss lower than 1.0 dB from the TM to TE polarization in a 200 nm wavelength range extending over C and L bands.

Low-loss high-speed silicon IQ modulator for QPSK/DQPSK in C and L bands.

A low-loss high-speed silicon in-phase (I) quadrature (Q) modulator is designed, fabricated and characterized. The fabricated IQ modulator has a low passive optical loss of 9 dB in C and L bands. Using the modulator, differential quadrature phase-shift keying (DQPSK) transmission at 44.6 Gb/s with differential detection is confirmed with an optical signal-to-noise ratio (OSNR) of 16.3 dB for a bit error rate (BER) of 10(-3) and a dispersion tolerance of -96 to 107 ps/nm. Moreover, in digital coherent detection, quadrature phase-shift keying (QPSK) up to 64 Gb/s are achieved with an OSNR of 11.6-11.8 dB for a BER of 10(-2) at 1530, 1550, and 1610 nm.

11-Gb/s 80-km transmission performance of zero-chirp silicon Mach-Zehnder modulator.

The 11-Gbps 80-km transmission performance of a zero-chirp silicon Mach-Zehnder modulator has been characterized. The zero-chirp characteristic of the silicon modulator is confirmed in the constellation measurement, and gives high tolerance both for positive and negative chromatic dispersion. A low-dispersion-penalty transmission up to 80 km using the 11-Gbps non return-to-zero on-off-keying format is confirmed via bit-error-rate measurements with a performance comparable to that of a commercial lithium-niobate modulator. The dispersion tolerance at 2-dB power penalty for a bit-error-rate of 10(-3) is more than ± 950 ps/nm. Further, 22.3-Gbps binary phase-shift-keying is demonstrated, and the back-to-back power penalty with respect to the lithium-niobate modulator is less than 0.5 dB.

Accurate magnetic field imaging using nanodiamond quantum sensors enhanced by machine learning.

Nanodiamonds can be excellent quantum sensors for local magnetic field measurements. We demonstrate magnetic field imaging with high accuracy of 1.8 [Formula: see text]T combining nanodiamond ensemble (NDE) and machine learning without any physical models. We discover the dependence of the NDE signal on the field direction, suggesting the application of NDE for vector magnetometry and the improvement of the existing model. Our method enhances the NDE performance sufficiently to visualize nano-magnetism and mesoscopic current and expands the applicability of NDE in arbitrarily shaped materials, including living organisms. This accomplishment bridges machine learning to quantum sensing for accurate measurements.

Silicon Mach-Zehnder modulator of extinction ratio beyond 10 dB at 10.0-12.5 Gbps.

Silicon Mach-Zehnder modulators with reduced series resistance in lateral PN junction rib-waveguide phase shifters for enhanced high-speed response are fabricated and characterized. Extinction ratio higher than 10 dB is obtained at 10.3-11.7 Gbps with mask margins of 27% (10.3-Gbps 10GBE), 16% (10.7-Gbps STM-64/OC-192) and 10% (11.3-Gbps STM-64/OC-192) in eye-diagram measurements incorporating mask tests using a RF cut-off filter. In unfiltered eye-diagram measurements without mask tests, extinction ratio higher than 13 dB is obtained at 10.0-12.5 Gbps. The silicon modulators reveal high-speed performance comparable with that of lithium-niobate modulators in high-speed optical fiber telecommunications.

New design and analysis of Bragg grating waveguides.

New design of optical waveguides is presented to synthesize Bragg grating waveguides without inducing birefringence. In the design, waveguide core has a thin trench on the top surface of the core and width of the trench is modulated concurrently with width modulation of the waveguide core. Effective refractive index profiles in Bragg grating waveguides are obtained by a differential inverse scattering algorithm and converted to waveguide width profiles by using the new core design. This procedure allows design of non-birefringent Bragg grating waveguides on planar substrate. The method is applied to the design of chromatic dispersion compensators. For characterization of Bragg grating waveguides, analysis based on short-time Fourier transform of Bragg grating response waveforms is presented.

Label-free detection of real-time DNA amplification using a nanofluidic diffraction grating.

Quantitative DNA amplification using fluorescence labeling has played an important role in the recent, rapid progress of basic medical and molecular biological research. Here we report a label-free detection of real-time DNA amplification using a nanofluidic diffraction grating. Our detection system observed intensity changes during DNA amplification of diffracted light derived from the passage of a laser beam through nanochannels embedded in a microchannel. Numerical simulations revealed that the diffracted light intensity change in the nanofluidic diffraction grating was attributed to the change of refractive index. We showed the first case reported to date for label-free detection of real-time DNA amplification, such as specific DNA sequences from tubercle bacilli (TB) and human papillomavirus (HPV). Since our developed system allows quantification of the initial concentration of amplified DNA molecules ranging from 1 fM to 1 pM, we expect that it will offer a new strategy for developing fundamental techniques of medical applications.

Real-time intuitive spectrogram measurement of ultrashort optical pulses using two-photon absorption in a semiconductor.

Real-time acquisition of intuitive spectrograms based on twophoton absorption frequency-resolved optical gating is demonstrated in a wavelength range around 1500 nm using an InP crystal for a two-photon absorption medium. Rapid wavelength-delay scanning, based on a counterrotating spectrometer mirror synchronized with a delay stage, is introduced and incorporated with lock-in detection for the real-time spectrogram acquisition. It is shown that the frequency marginal and average delay time of acquired spectrograms provide the spectral intensity and group delay time of optical pulses under test. This allows the direct and rapid measurement of the magnitude and phase of ultrashort optical pulses in the spectral domain without using pulse retrieval algorithms to reconstruct the pulse shapes.

Characterization of chromatic dispersion of optical filters by high-stability real-time spectral interferometry.

Chromatic dispersion of optical filters is characterized by what is believed to be novel broadband spectral interferometry, which is based on dual-wavelength heterodyne measurement of spectral phase. High phase stability is achieved by differential phase detection using two lasers for wavelength-swept probe and phase-tracking reference. The technique provides self-tracking interferometry by passive stabilization of optical phase and allows real-time measurement of spectral phase and group delay with a low phase drift of less than 0.04pi. A fiber Bragg grating and a thin-film filter are characterized by this method.