Yi-Shin Su

Influence of separate confinement heterostructure layer on carrier distribution in InGaAsP laser diodes with nonidentical multiple quantum wells

The thickness of the separate confinement heterostructure (SCH) layer is found to have a significant influence on the carrier distribution among InGaAsP multiple quantum wells in laser diodes. When the SCH layer is 120 nm thick, the carrier distribution of the fabricated laser diodes favors quantum wells near the n-cladding layer. When the thickness of the SCH layer is reduced to 20 nm, the carrier distribution of the fabricated laser diodes favors quantum wells near the p-cladding layer. Our experiments indicate that the carrier distribution of a fabricated laser diode can be engineered using an SCH layer of appropriate thickness.

External-cavity semiconductor laser tunable from 1.3 to 1.54 μm for optical communication

Using semiconductor optical amplifiers with properly designed nonidentical quantum wells made of InGaAsP-InP materials in the external-cavity configuration, the semiconductor laser is broadly tunable. The tuning range covers from 1.3 /spl mu/m to 1.54 /spl mu/m. Without additional filtering techniques, the laser beam emitted from the linear external cavity has the sidemode suppression ratio better than 30 dB. Also, the power ratio of the lasing mode to the total output power is 90%-99%, indicating the dominance of the lasing mode in the amplification process due to the broad gain spectrum.

Influence of separate confinement heterostructure on emission bandwidth of InGaAsP superluminescent diodes/semiconductor optical amplifiers with nonidentical multiple quantum wells

Experiments show that the layer of separate confinement heterostructure (SCH) has a significant influence on the emission spectrum of superluminescent diodes (SLDs)/semiconductor optical amplifiers (SOAs). Reducing the thickness of SCH layer at the p-side could improve the uniformity of carrier distribution among multiple quantum wells (MQWs). With three In/sub 0.67/Ga/sub 0.33/As/sub 0.72/P/sub 0.28/ QWs near the p-side and two In/sub 0.53/Ga/sub 0.47/As QWs near the n-side, when the thickness of the SCH layer changes from 120 to 30 nm, the operation current for SLDs/SOAs to exhibit the full-width at half-maximum spectral width of above 270 nm could be reduced from 500 to 160 mA.

174-nm mode spacing in dual-wavelength semiconductor laser using nonidentical InGaAsP quantum wells

A very wide tuning range of dual-wavelength semiconductor lasers with properly designed nonidentical InGaAsP quantum wells is reported. As the external cavity of reflected-type grating telescope configuration is well aligned, the dual-wavelength operation can be achieved with a record wavelength separation as large as 174 nm (25 THz). The wide separation of two wavelengths is possible due to a proper modification of the external-cavity configuration and reduced gain competition of laser modes.

High-power angled broad-area 1.3-/spl mu/m laser diodes with good beam quality

A new type of high-power laser diodes is fabricated with a broad-area waveguide tilted at 7/spl deg/ from the facet normal. For the current between 0.6 and 1.2 A, it behaves like a superluminescent diode with 40-nm spectral width and 40-mW output power. The far field emits at about 25/spl deg/ away from the facet normal. For the current above 1.2 A, it oscillates with a narrow spectrum. The far field emits along the facet normal with its angle only twice of the diffraction limit. The output power per facet could be 1 W at 12 A.

Improved temperature characteristics of laser diodes with nonidentical multiple quantum wells due to temperature-induced carrier redistribution

Laser diodes with nonidentical multiple quantum wells could have the lasing wavelength very insensitive to temperature variation. For temperature varying from 33 to 260 K, the lasing energy changes less than 5 meV, while the band gap energy changes more than 50 meV. The origin is due to the strongly temperature-dependent Fermi–Dirac distribution, which favors carriers in high-energy states at large temperature. The temperature-induced carrier redistribution could even cause negative characteristic temperature for a certain temperature range because the low-energy quantum wells behave like reservoirs to overcome the detrimental influence of temperature.

Anticompetition of laser modes

Anticompetition of laser modes is observed. In this behavior, the increase of intensity in one lasing mode could enhance the intensity of another mode, which is opposite to the usual competition behavior and so-called anticompetition. In our experiments using the semiconductor laser with very broadband gain medium, anticompetition exists when the laser modes have their wavelengths widely separated. Anticompetition can be observed for spectral separation of 138 nm and is even more prominent for spectral separation up to 167 nm. Theoretical analysis shows that anticompetition is due to the physics similar to optical pumping.

Opposite temperature effects of quantum-dot laser under dual-wavelength operation

The authors discover opposite temperature effects when the quantum-dot (QD) laser is controlled to simultaneously oscillate at two modes in the external cavity. The two modes correspond to the ground state and the first excited state of the QDs. Experiments show that the power of one mode increases, while the power of the other mode decreases as the temperature increases. The power variation between these two modes is similar to the situation of competition and anticompetition of laser modes. The physical reason is discussed in detail.

Investigation of laser-mode anticompetition in semiconductor lasers

Influential factors of laser-mode anticompetition are investigated in dual-wavelength semiconductor laser. Experiment shows that with increasing wavelength, separation, or decreasing initial power of the long-wavelength mode (LWM), the slope of the anticompetition curve and the maximum power increment of the LWM increase. Under fixed wavelength separation, anticompetition can exist only when the power of the short-wavelength mode (SWM) is below a certain level. In addition, the wavelength position has an effect on anticompetition. Different injection current also results in different behaviors of anticompetition. Anticompetition can only be observed with varying the power of the SWM.

Extremely broadband superluminescent diodes/semiconductor optical amplifiers in optical communication band

Superluminescent diodes with broad emission bandwidth characteristics and the mechanism of carrier distribution in the active layer are explored. Asymmetric active layer structure is used for the broadband purpose. Using InP substrate with five 60Å InGaAsP quantum wells and two 150Å InGaAs quantum wells, we get a very broad emission spectrum. The spectral width is nearly 400 nm, almost covering the range from 1250nm to 1650nm.