Chia-Wei Tsai

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.

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.

Broadband semiconductor optical amplifiers and tunable semiconductor lasers

Nonidentical multiple quantum wells (MQWs) had been widely used for broadening the emission or gain bandwidth of semiconductor optical amplifiers (SOAs). However, the carrier distribution among the MQWs is not uniform, leading to nonuniform gain contributed from different QWs. Thus using nonidentical MQWs for broadband purpose is not intuitively straightforward. Several factors need to be carefully considered. Those factors include the QW sequence, electron/hole transport time across the separate confinement hetero-structure, as well as carrier capture time. In this work, we will discuss the design of MQWs for broadband SOAs. With properly designed nonidentical MQWs, the emission bandwidth could be nearly 400 nm. Also, the tuning range of semiconductor lasers could be extended to be over 200 nm.

Glass-clad crystal fibers based ultrahigh resolution optical coherence tomography

Active crystal fibers can generate CW and near-Gaussian-shape milliwatt-level broadband emissions at 560 nm, 770 nm, and 1380 nm with 3-dB bandwidths of 98, 210, and 240 nm, respectively. They are eminently suitable for ultrahighresolution optical coherence tomography.

Glass-clad crystal fiber based ultra-high resolution optical coherence tomography

Cr4+:YAG double-clad crystal fiber can generate CW and near-Gaussian-shape 265-nm emission at milliwatt level. I will describe our work on a cellular resolution optical coherence tomography, which has a 3.6-μm axial resolution at NIR wavelength in air.

Energy up conversion caused by metallic photonic boxes

A photonic box structure is discovered to have the characteristic of transferring part of the input pumping 532nm laser energy to wavelength 300nm. The spectral width is narrower and the intensity is linearly increased as the intensity of the input laser increases. The spectral width shows an abrupt change when input laser power exceeds 30mW. The mechanism of this phenomenon is considered to be related to surface plasmon resonance, however, complete explanation cannot be obtained through known physics. This new energy transfer phenomenon gives us a new direction toward using the photonic box structure.

Angled broad-area semiconductor lasers to emit high output power with good beam quality

A new type of laser diodes with good beam quality is introduced. The far-field divergence angle can be close to diffraction-limited value. In the new design, the direction of the waveguide on a broad area Fabry-Perot laser diode is tilted at an angle from the facet normal. This design is called “angled broad area laser diode”. In this tilted waveguide device, filamentation is not observed. The far-field divergence angle is generally within 5 times the diffraction-limited value. This tilted broad area laser is advantageous over the angled grating DFB laser because the difficulty of matching the grating period with peak gain wavelength is avoided.

High-power semiconductor laser with diffraction-limited output beam

High-power semiconductor lasers could be used as pumping sources for solid-state lasers, fiber lasers, Raman lasers, and for material processing and medicine applications, etc. In this work, we discover a new broad-area waveguide structure that could result in high output power with diffraction-limited beam. The structure has the broad-area waveguide similar to the conventional broad-area laser diodes, but the waveguide is aligned at 7/spl deg/ from the normal of the cleaved facets. The waveguide is very broad. The width is 100 /spl mu/m. Its length is 1.5 mm.

Extremely broadband InGaAsP/InP superluminescent diode/semiconductor optical amplifiers with emission spectrum covering from 1250 nm to 1650 nm

Using five 60A InGaAsP quantum wells and two 150A InGaAs quantum wells for superluminescent diodes, we obtain a very broad emission spectrum. The spectral width is nearly 400nm, covering the range from 1250nm to 1650nm.