Genji Tohmon

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>>

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.

Hybridly integrated optical transceiver module for access networks

Hybridly integrated optical transceiver modules for 1.3 /spl mu/m wavelength TDM (Time-Division-Multiplexing) bi-directional transmission and 1.3/1.55 /spl mu/m WDM (Wavelength-Division-Multiplexing) bi-directional transmission are demonstrated. Surface mounted laser diode and PIN photodiode are passively aligned to a fiber-embedded optical circuit. The module consists of a transmitting 1.3 /spl mu/m laser diode mounted on a silicon substrate with a V-groove for fiber attachment and a receiving photodiode surface mounted onto a glass substrate which has embedded in it a single mode fiber for input/output. Either power splitting 3 dB filter or wavelength selective WDM filter (1.55 /spl mu/m reflective) is inserted into the embedded fiber which directs the incoming signal light to the photodiode. The optical transceiver characteristics are as follows. The output power was greater than 2 mW for TDM transceiver and 4 mW for WDM transceiver, considering a 20% coupling efficiency to the single mode fiber. The responsivity of the photodiode were 0.97 A/W for WDM transceiver at 1.55 /spl mu/m, and 0.46 A/W for TDM transceiver at 1.3 /spl mu/m. Stable operation characteristics are obtained in the wide temperature range of -40/spl sim/85/spl deg/C.

Wavelength stability of DFB lasers for non-hermetic applications

As the opto-electronics telecommunication components industry moves toward higher speed, lower cost packages, with higher and higher levels of integration, the need for non-hermetic distributed feedback (DFB) laser diodes has arrived. As an example, we have integrated these laser diodes into non-hermetic 2.5 Gbit/s transponder samples, which have demonstrated 20-kilometer link distances. We consider here DFB lasers for non-hermetic telecommunication applications. One of the critical issues facing non-hermetic laser diodes involves proper passivation of the laser facet region to prevent electro-chemical corrosion of the InP semiconductor material. One approach involves the use of a polymer encapsulent to protect the laser diode from electrochemical corrosion induced by moisture. However, polymer encapsulent does not inhibit moisture penetration, and may only passivate the laser diode at the junction region. Our approach involves the use of an Al/sub x/Ta/sub y/O/sub z/ facet coating that inhibits the absorption of moisture and serves as both a back (highly reflective) and front (antireflective) coating. For the non-hermetic DFB laser, we are concerned with not only moisture penetration and facet coating delamination, but also wavelength stability which is highly sensitive to changes in facet coating refractive index. We have examined the power aging and wavelength stability of non-hermetic DFB lasers with two different Al/sub x/Ta/sub y/D/sub z/ facet coatings under temperature/humidity/bias (THB) conditions. Small populations of lasers have been subjected to 85 C/85% RH conditions under low bias (/spl sim/10 mA) conditions. It is extremely important to accelerate the effects of moisture and humidity in these laser diodes to ensure that they remain robust for 15-20 years in non-hermetic environments. Low bias prevents the laser junction region from heating up with respect to the local ambient, yet still provides ample potential (/spl sim/1V) to promote any electro-chemical corrosion effects. The use of low current effectively prevents the laser from drying out (which will drastically lower the relative humidity at the junction region) and generating false negative results. Data is provided on wavelength and power stability of nonhermetic DFB lasers subjected to accelerated THB conditions. To our knowledge this is the first reported data on wavelength stability of non-hermetic DFB lasers in hot humid ambients.

Novel 1.3/1.55 /spl mu/m dual-wavelength receiver having embedded fiber circuit for optical subscriber systems

Summary form only given. We propose and demonstrate a novel dual-wavelength receiver, which has an embedded fiber circuit that demultiplexes 1.3- and 1.55-/spl mu/m signals to separate photodiodes mounted on a single-substrate surface. The circuit contains wavelength separation filters placed in slits fabricated in the fiber path by a conventional cutting saw. Low-circuit loss and high-receiver performance is realized for both WDM signals.

Fluoride-based fiber lasers: prospects for the future

Rare earth ion doped fiber devices can achieve high efficiencies and high output powers due to their advantages of high optical pump power densities over long interaction lengths. With the advent of fluoride-based fibers, breakthroughs into both the short- and long-wavelength regions not possible with silica-based fibers have achieved. The low phonon energy and high rare earth ion doping concentrations of fluorides allow multi-level transition processes such as upconversion. This paper reviews some of the recent advances in fluoride-based fiber lasers and amplifiers, and takes a look at the major issues, mainly from an industrial viewpoint. The primary issue of cost has hampered commercialization and widespread acceptance of these devices. The future prospects of fluoride-based fiber devices will be discussed from the viewpoint of industrial applications.

Hybrid integration of 1.3-/spl mu/m transmitter and 1.55-/spl mu/m receiver with fiber-embedded circuit

The high cost of manufacturing multiwavelength optical transmitter and receiver components is one of the biggest hindrances to widespread acceptance of wavelength-division multiplexing (WDM) optical subscriber loop networks for broadband multimedia systems. One proposed solution is to passively align laser diodes and photodiodes to waveguides in a circuit-like structure. We have previously proposed the use of a fiber-embedded circuit for a WDM receiver module. Because the fiber-embedded circuit is an in-line device, as opposed to a line-terminating device, this approach can be extended to include a passively aligned LD for the transmitter function. We demonstrate a novel WDM transceiver module with a hybridly integrated 1.3-/spl mu/m laser diode and 1.55-/spl mu/m PIN photodiode, which were passively aligned to a fiber-embedded circuit. Transmission output power >1.5 mW and detector responsivity of 0.8 A/W were obtained.