Jun Ohya

Picosecond blue light pulse generation by frequency doubling of a gain‐switched GaAlAs laser diode with saturable absorbers

Picosecond blue light pulse generation by frequency doubling of a gain‐switched GaAlAs laser diode in a proton‐exchanged MgO:LiNbO3 waveguide is reported. High‐peak fundamental pulse power of 1.23 W is obtained by employing a laser diode with saturable absorbers. Blue light pulse of 7.88 mW maximum peak power and 28.7 ps pulse width is generated in the form of Cherenkov radiation.

Generation of ultraviolet picosecond pulses by frequency-doubling of laser diode in proton-exchanged MgO:LiNbO/sub 3/ waveguide

Ultraviolet picosecond pulses were generated by frequency doubling a AlGaAs-GaAs laser diode in a proton-exchanged waveguide fabricated in MgO:LiNbO/sub 3/. The Cerenkov radiation scheme was used to phase-match the infrared pulse from a gain-switched laser diode, which operates in multilongitudinal modes. Pulses with a peak power of 1.35 mW and 19.3-ps width were obtained at 390 nm. This is a unique method for generating short ultraviolet pulses with laser diodes in a simple configuration.<<ETX>>

Spectral linewidth and resonant frequency characteristics of InGaAsP/InP multiquantum well lasers

The spectral linewidth and resonant frequency characteristics of 1.3- mu m InGaAsP/InP multi-quantum-well lasers grown by liquid-phase epitaxy were investigated and compared to those of the conventional double heterostructure (DH) lasers. A decrease in spectral linewidth and an increase in resonant frequency f/sub r/ with decreasing well thickness were observed. Moreover, the linewidth enhancement factor alpha was reduced to approximately 2 for well thicknesses of less than approximately 200 AA, while that of the DH laser was approximately 6. An f/sub r/ of 9 GHz, which is twice as large as that of conventional DH lasers, was achieved at an optical power of 5.3 mW/facet. >

Single longitudinal mode operation of long, integrated passive cavity InGaAsP lasers

We propose a new 1.3‐μm wavelength InGaAsP laser—the integrated passive cavity (IPC) laser—and demonstrate its device performances compared with conventional lasers fabricated under similar procedures. The long IPC laser (3.55‐mm‐long passive cavity), as well as the short IPC laser, exhibited single frequency oscillation even just above the threshold, and the maximum ratio of longitudinal main to submode exceeded 30 dB. They also showed favorable effects in the oscillation frequency stabilization.

Second-order distortion generated by amplification of intensity-modulated signals with chirping in erbium-doped fiber

A rate equation analysis for second-order distortion generated in an erbium-doped fiber amplifier is reported. It is shown that the relevant mechanism of distortion is the interaction between the frequency chirping of input light and the local gain tilt in the erbium-doped fiber. It is found that the output light distortion is highly affected by the phase difference between the input light distortion and the chirping-induced distortion. This indicates that second-order distortion is not always degraded by erbium-doped fiber amplifiers.<<ETX>>

Correlation between intensity noise and longitudinal modes of a semiconductor laser coupled to an external cavity

Correlation between intensity noise and fine structures of longitudinal modes in a semiconductor laser coupled to an external cavity has been investigated. It is experimentally shown that the intensity noise is perfectly suppressed when the laser oscillates in ‘‘pure’’ single frequency oscillation even with strong optical feedback. Intensity noise, which arises only when several external cavity modes exist, is interpreted in terms of the time‐dependent refractive index in the semiconductor cavity caused by the light beatings among the lasing modes.

Generation of picosecond blue light pulse by frequency doubling of gain-switched GaAlAs laser diode having saturable absorber

Picosecond pulse generation of blue light by frequency doubling of a GaAlAs laser diode is reported. High power pulse generation is realized by incorporating gain switching of a laser diode with a saturable absorber and frequency doubling in a proton-exchanged MgO:LiNbO/sub 3/ waveguide. The laser diode with a longer saturable absorber can produce optical pulses with higher peak power and narrower pulse width. The spectral bandwidth of second-harmonic generation for the waveguide is evaluated at about 20 nm. This is wide enough to frequency-double all the multilongitudinal modes of the gain-switched laser diode. A blue light pulse of 7.88-mW maximum peak power and 28.7-ps pulsewidth is obtained for a 1.23-W peak pulse of the laser diode. >

Thulium:ZBLAN blue fiber laser pumped by two wavelengths

We demonstrate and analyze an upconversion blue fiber laser pumped by two wavelengths. Lasing at 0.48 mum with very low pump threshold power is obtained from a Tm-doped fluorozirconate fiber that is counterpropagating pumped by 1.21- and 0.649-mum light. We employed a rate-equation analysis using parameters obtained by fitting to the experimental data to predict the 0.48-mum output characteristics as a function of fiber length and output reflectivity.

Energy transfer in Tm:Eu codoped fluorozirconate fiber

Excited state absorption‐induced up conversion at 452 and 480 nm in Tm:Eu:ZBLAN fiber was observed for a single pump laser source at 650 nm. Compared to Tm:ZBLAN fiber, codoping with Eu3+ increases the 452 nm emission while the 480 nm emission is reduced. The effective lifetime of the terminal 3H4 level of the 452 nm transition in Tm3+ is shortened by energy transfer to the 7F6 level in Eu3+. This energy transfer scheme is useful in discriminating radiative transitions.

Cancellation of second-order distortion of directly modulated laser in erbium-doped fiber amplifier

Experimental verification of cancellation of second-order distortion from a directly modulated laser diode by amplification in an erbium-doped fiber is demonstrated. This cancellation occurs when the distortion of laser diode and the distortion generated in the erbium-doped fiber amplifier are out of phase. >