Temperature-independent lasing wavelength of highly stacked InAs quantum dot laser fabricated on InP(311)B substrate with Bi irradiation.

In this study, the effects of bismuth (Bi) irradiation on InAs quantum dot (QD) lasers operating in the telecommunication wavelength band were investigated. Highly stacked InAs QDs were grown on an InP(311)B substrate under Bi irradiation, and a broad-area laser was fabricated. In the lasing operation, the threshold currents were almost the same, regardless of Bi irradiation at room temperature. These QD lasers were operated at temperatures between 20 and 75°C, indicating the possibility of high-temperature operation. In addition, the temperature dependence of the oscillation wavelength changed from 0.531 nm/K to 0.168 nm/K using Bi in the temperature range 20-75°C.

Polarization division multiplexed 4 × 10 Gbps simultaneous transmissions in 1.0-µm waveband and C-waveband over a 14.4-km-long holey fiber using an ultra-broadband photonic transport system.

Polarization division multiplexing (PDM) and wavelength division multiplexing (WDM) are essential techniques for enhancing the capacity of photonic networks and facilitating the efficient use of optical frequency resources. 2 PDM × 2 WDM × 10 Gbps error-free simultaneous transmissions in the 1.0-µm waveband and C-waveband are successfully demonstrated for the first time using an ultra-broadband photonic transport system over a 14.4-km-long holey fiber transmission line.

Narrow-line-width 1.31-µm wavelength tunable quantum dot laser using sandwiched sub-nano separator growth technique.

A wide wavelength tunable quantum dot (QD) external cavity laser operating in the 1.31-µm waveband with a narrow line-width is successfully demonstrated. A high-density, high-quality InAs/InGaAs QD optical gain medium for the 1.31-µm waveband was obtained using a sandwiched sub-nano separator growth technique. A wide wavelength tunability of 1.265-1.321 µm and a narrow line-width of 210 kHz were successfully achieved using a compact and robust external cavity system constructed with multiple optical band-pass and etalon filters for active optical mode selection. The laser also achieved an error-free 10-Gb/s photonic data transmission over an 11.4-km-long holey fiber.

Simultaneous 3 x 10 Gbps optical data transmission in 1-mum, C-, and L-wavebands over a single holey fiber using an ultra-broadband photonic transport system.

An ultra-broadband photonic transport system has been developed to expand the usable wavelength bandwidth for optical communication. Simultaneous 3 x 10-Gbps error-free photonic transmissions are demonstrated in the 1-microm, C-, and L-wavebands by using the ultra-broadband photonic transport system over a 5.4-km-long holey fiber transmission line.

Ultrafast and broadband frequency chirp signal generation using a high-extinction-ratio optical modulator.

We successfully demonstrate ultrafast frequency sweep signal generation using the double-sideband suppressed carrier modulation technique with a high-extinction-ratio optical modulator that helps realize clear signals with no filters. The resultant sweep rate was achieved at 3.67 × 10(16) Hz/s with an extinction ratio above 25 dB, which corresponds to a bandwidth of 11 GHz with a pulse duration of 300 ns.

10-Gbps, 1-microm waveband photonic transmission with a harmonically mode-locked semiconductor laser.

To open up a 1-microm waveband for photonic transport systems, we developed a hybrid and harmonically mode-locked semiconductor laser (MLL) that can transmit return-to-zero (RZ) optical signals at data rates on the order of gigabits per second. A single-mode hole-assisted fiber (HAF) was also developed for use as a 1-microm waveband signal transmission line. A stable optical pulse train with a repetition rate of 9.953 GHz, pulse width of 22 ps, and low timing jitter of 120 fs was obtained from a 1035-nm harmonically MLL. With these devices, we successfully demonstrated 1-microm waveband error-free transmission of a high-speed 10-Gbps RZ signal over a long distance of 7 km.

Nano-scale photonic crystal microcavity characterization with an all-fiber based 1.2 - 2.0 mum supercontinuum.

The use of ultra-broadband supercontinuum generated by an all-fiber system to characterize high-index contrast photonic circuits over the wavelength range 1.2 - 2.0 microm is demonstrated. Efficient, broadband waveguide coupling techniques and sensitive normalized detection enable rapid and high-resolution measurements of nano-scale one-dimensional photonic crystal microcavities. Experimental mappings of bandgaps and cavity mode resonances with a wavelength resolution of 0.1 nm compare well with computer simulations.

Highly nonlinear bismuth-oxide fiber for smooth supercontinuum generation at 1.5 microm.

Short lengths of highly nonlinear bismuth-oxide fiber are used to generate smooth supercontinuum spanning from 1200 nm to 1800 nm, with sub-0.5 nJ pulse energies. The spectral broadening in a 2-cm length of this fiber was used to compress 150-fs pulses to 25 fs.

Broadband wavelength-tunable ultrashort pulse source using a Mach-Zehnder modulator and dispersion-flattened dispersion-decreasing fiber.

The broadband wavelength tunability of femtosecond pulse generation using a Mach-Zehnder-modulator-based flat-comb generator (MZ-FCG) and a dispersion-flattened dispersion-decreasing fiber (DF-DDF) was demonstrated. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond pulses by adiabatic soliton compression. By tuning the wavelength of the input cw light, 200 fs, 10 GHz pulses were generated in the wavelength range of 1,535 to 1,570 nm. Such wide-range wavelength tunability was realized by both the independence of a comb-flattening condition from the inputted wavelength and the dispersion flatness of the DF-DDF.

Tunable all-optical pulse compression and stretching via doublet Brillouin gain lines in an optical fiber.

We demonstrate tunable all-optical pulse compression and stretching via doublet Brillouin gain lines in an optical fiber. Tunable pulse compression or a stretching ratio of 1.47-0.43 accompanying a time delay is achieved by controlling the separation between two gain lines, for an input pulse train with a 40 ns width and a repetition rate of 5 MHz, in a 4 km silica fiber with a fixed pump power of 88.1 mW. The limitation of this pulse compressor or stretcher is also discussed.

Widely repetition-tunable 200 fs pulse source using a Mach-Zehnder-modulator-based flat comb generator and dispersion-flattened dispersion-decreasing fiber.

By combining a Mach-Zehnder-modulator-based flat comb generator (MZ-FCG) with a dispersion-flattened dispersion-decreasing fiber, femtosecond pulses have been generated from a cw light. Near-Fourier-transform-limit picosecond pulses generated from the MZ-FCG were compressed into femtosecond order by pulse compression. Our system enables flexible tuning of the repetition rate and pulse width, because those depend on the driving signal of the MZ-FCG. Pulse trains of 200 fs width were continuously and stably generated without mode hopping, with a repetition rate range from 5 to 17 GHz. Our system consists of a modulator and compression fiber; thus, the configuration is simpler and more stable.

Ultrafast walk-off-free nonlinear optical loop mirror by a simplified configuration for 320-Gbit / s time-division multiplexing signal demultiplexing.

We demonstrate a simplified configuration of an ultrafast walk-off-free nonlinear optical loop mirror (NOLM) for 320-10-Gbit/s optical time-division demultiplexing. The proposed NOLM consists of a short, 100-m length of highly nonlinear dispersion-shifted fiber, resulting in compact, highly stable, and ultrafast walk-off-free operation.