Hiroaki Sanjoh

Optical orthogonal frequency division multiplexing using frequency/time domain filtering for high spectral efficiency up to 1 bit/s/Hz

Summary form only given. We have proposed a novel optical orthogonal frequency division multiplexing technique that can overcome the spectral efficiency limitation of the conventional WDM system. This scheme permits substantial overlapping of the spectrum and can achieve the spectral efficiency up to 1 bit/s/Hz in principle. For demultiplexing, we used a newly developed optical discrete Fourier transformer (DFT) instead of electrical digital processing, which is impossible to apply in the optical frequency range. The optical DFT was realized by using a set of delay lines, a phase shifter and a coupler in the frequency domain and bit synchronization and an optical gate in the time domain. In experimental demonstration of this scheme, error-free operation was obtained with a 0.8 bit/s/Hz of spectral efficiency.

Multiwavelength light source with precise frequency spacing using a mode-locked semiconductor laser and an arrayed waveguide grating filter

A multiwavelength light source with precise optical frequency spacing can be created by extracting an individual mode of a semiconductor mode-locked laser using an arrayed waveguide grating filter. The outputs of the light source are locked to wavelength division multiplexing (WDM) optical frequency grids using an optical frequency standard light source. They can be successfully modulated by 5 Gb/s nonreturn-to-zero (NRZ) signals and can be transmitted through 100-km-long optical fiber.

50-Gb/s Direct Modulation of a 1.3-μm InGaAlAs-Based DFB Laser With a Ridge Waveguide Structure

We demonstrate 50-Gb/s direct modulation by using 1.3-μm distributed-feedback lasers with a ridge waveguide structure. We employed InGaAlAs material for a multiple-quantum well to obtain a low damping factor K, and fabricated a ridge waveguide structure buried in benzocyclobutene to realize a structure with a low parasitic capacitance. In addition, to obtain high maximum frequency relaxation oscillations fr, we designed the cavity length L), and achieved a 3-dB-down frequency bandwidth of 34 GHz. We realized 50-Gb/s clear eye openings with a back-to-back configuration, and achieved a mean output power of over 5.0 dBm, and a dynamic extinction ratio of 4.5 dB. We measured the 50-Gb/s transmission characteristics, and obtained clear eye openings for transmissions over 20-, 40-, and 60-km single-mode fibers (SMF). We also measured the bit-error-rate performance, and obtained an error-free operation and a power penalty of less than 0.5 dB after a 10-km SMF transmission.

Ultra-Compact 100 GbE Transmitter Optical Sub-Assembly for 40-km SMF Transmission

The first ultra-compact transmitter optical sub-assembly (TOSA) has been developed for the metro-area 100 Gbit/s Ethernet (100 GbE) system. Four DFB lasers integrated with electro-absorption modulators (EADFB lasers) operated at 25.8 Gbit/s and an optical multiplexer are monolithically integrated on one chip. The chip was assembled in the compact TOSA using a three-dimensional (3D) RF circuit board supported by a spacer. The new structure provides compact and high-density interconnection with low crosstalk between RF signal lines. The TOSA is very small at just 8.0 mm × 35 mm × 6.5 mm including the receptacle and the flexible printed circuit (FPC) and could be installed in next-generation small form 100 GbE transceivers. In addition, an error-free transmission is demonstrated through 40 km of single-mode fiber at 100 Gbit/s with a modulation voltage of 2 V.

Packaged polarization-insensitive WDM monitor with low loss (7.3 dB) and wide tuning range (4.5 nm)

Low-cost high-performance wavelength-division-multiplexing (WDM) monitors and receivers are key components in WDM transmission and local area optical networks. A semiconductor arrayed waveguide grating integrated with a photodiode is attractive because of its small size and simple fabrication process. A low-loss (7.3 dB) polarization-insensitive packaged WDM monitor has been fabricated in an industry-standard butterfly-type module. The eight-channel monitors, which have 200-GHz channel spacing, can be tuned simultaneously in the 4.5-nm range.

80-Gb/s Low-Driving-Voltage InP DQPSK Modulator With an n-p-i-n Structure

We present a traveling-wave-electrode InP-based differential quadrature phase-shift keying modulator with a novel n-p-i-n waveguide structure. The structure features low electrical and optical propagation losses, which allow the modulator to operate at a high bit rate together with a low driving voltage and a low insertion loss. We successfully demonstrate 80-Gb/s modulation with a driving voltage of only 3 Vpp in a push-pull configuration. The chip size is just 7.5 mm times 1.3 mm.

Monolithically integrated WDM channel selectors on InP substrates

8-channel WDM channel selectors were fabricated on InP substrates. A compact device size of 5.2 mm/spl times/3.6 mm is achieved with a combination of deep-ridge waveguides and buried waveguides. The device can select an arbitrary signal from WDM signals with a low crosstalk of less than -40 dB.

Zero insertion loss operations in monolithically integrated WDM channel selectors

Eight-channel wavelength-division-multiplexed (WDM) channel selectors were fabricated based on an monolithic integration of two arrayed-waveguide gratings and a semiconductor optical amplifier array on InP substrates. A compact device size of 5.2/spl times/3.6 mm/sup 2/ was achieved with a combination of deep-ridge waveguides and buried waveguides. The device can select an arbitrary signal from a WDM signal with a low crosstalk of less than -40 dB, and fiber-to-fiber zero insertion loss operations were also achieved.

Measurement of phase and amplitude error distributions in arrayed-waveguide grating multi/demultiplexers based on dispersive waveguide

We measured the phase and amplitude error distributions in InP-based arrayed-waveguide grating (AWG) multi/demultiplexers using Fourier transform spectroscopy with interferogram restoration. The interferogram restoration was used to reduce the effect of the group-velocity dispersion of the waveguide. It was based on a wavenumber scale transformation or a dispersion balance between two arms in the interferometer. We derived a criterion for choosing the appropriate restoration method by estimating the worst-case measurement error in the presence of second order dispersion. After selecting a method using the derived criterion, we obtained isolated fringe patterns, from which we were able to obtain the phase and amplitude distributions in 50 and 200 GHz AWGs. Using the obtained distributions, we examined the origin of the crosstalk and chromatic dispersion in InP-based AWGs. The results revealed that the main origin is phase error as found with SiO/sub 2/-based AWGs.

Multiwavelength light source with precise frequency spacing using mode-locked semiconductor laser and arrayed waveguide grating filter

We report here a multiwavelength light source using semiconductor mode-locked lasers with the optical frequency spacing of 100 GHz. In this light source, a mode-locked semiconductor laser was used for the original light source, which gave multimodes with constant frequency spacings. The output from the mode-locked laser was fed into silica-based arrayed waveguide grating filter (AWG) with the free spectral range of 100 GHz and 16 channels of input/output ports.A multiwavelength light source with precise optical frequency spacing can be created by extracting an individual mode of a semiconductor mode-locked laser using an arrayed waveguide grating filter. The outputs of the light source are locked to wavelength division multiplexing (WDM) optical frequency grids using an optical frequency standard light source. They can be successfully modulated by 5 Gb/s nonreturn-to-zero (NRZ) signals and can be transmitted through 100-km-long optical fiber.