Bocang Qiu

Monolithic integration via a universal damage enhanced quantum-well intermixing technique

A novel technique for quantum-well intermixing is demonstrated, which has proven a reliable means for obtaining postgrowth shifts in the band edge of a wide range of III-V material systems. The technique relies upon the generation of point defects via plasma induced damage during the deposition of sputtered SiO/sub 2/, and provides a simple and reliable process for the fabrication of both wavelength tuned lasers and monolithically integrated devices. Wavelength tuned broad area oxide stripe lasers are demonstrated in InGaAs-InAlGaAs, InGaAs-InGaAsP, and GaInP-AlGaInP quantum well systems, and it is shown that low absorption losses are obtained after intermixing. Oxide stripe lasers with integrated slab waveguides have also enabled the production of a narrow single lobed far field (3/spl deg/) pattern in both InGaAs-InAlGaAs, and GaInP-AlGaInP devices. Extended cavity ridge waveguide lasers operating at 1.5 /spl mu/m are demonstrated with low loss (/spl alpha/=4.1 cm/sup -1/) waveguides, and it is shown that this loss is limited only by free carrier absorption in waveguide cladding layers. In addition, the operation of intermixed multimode interference couplers is demonstrated, where four GaAs-AlGaAs laser amplifiers are monolithically integrated to produce high output powers of 180 mW in a single fundamental mode. The results illustrate that the technique can routinely be used to fabricate low-loss optical interconnects and offers a very promising route toward photonic integration.

Design and fabrication of low beam divergence and high kink-free power lasers

We report the design and fabrication of high performance high power lasers with emission wavelength from 800 to 1000 nm using a novel wafer structure, in which a graded V-shape layer was incorporated, to reduce the vertical far field (wafer growth direction) and to suppress higher order mode lasing. The structure offers the freedom to independently design the vertical far field and optical overlap with the quantum wells. An extremely low far field can be achieved, which still retains high optical overlap, allowing a low threshold current to be maintained. In addition, the structure can greatly enhance the laser kink-free power by suppressing or even completely eliminating higher order mode lasing, an extremely desirable property for high power single mode lasers.

High channel count and high precision channel spacing multi-wavelength laser array for future PICs

Multi-wavelength semiconductor laser arrays (MLAs) have wide applications in wavelength multiplexing division (WDM) networks. In spite of their tremendous potential, adoption of the MLA has been hampered by a number of issues, particularly wavelength precision and fabrication cost. In this paper, we report high channel count MLAs in which the wavelengths of each channel can be determined precisely through low-cost standard μm-level photolithography/holographic lithography and the reconstruction-equivalent-chirp (REC) technique. 60-wavelength MLAs with good wavelength spacing uniformity have been demonstrated experimentally, in which nearly 83% lasers are within a wavelength deviation of ±0.20 nm, corresponding to a tolerance of ±0.032 nm in the period pitch. As a result of employing the equivalent phase shift technique, the single longitudinal mode (SLM) yield is nearly 100%, while the theoretical yield of standard DFB lasers is only around 33.3%.

Monolithic fabrication of 2 /spl times/ 2 crosspoint switches in InGaAs-InAlGaAs multiple quantum wells using quantum-well intermixing

In this letter, we report the fabrication of 2 /spl times/ 2 crosspoint switches, which monolithically integrate passive waveguides, electro-absorption modulators and optical amplifiers onto one chip using sputtered SiO/sub 2/ quantum-well intermixing technique. The switches have low insertion loss to be about 4-5 dB and extinction ratios up to 26 dB.

Low divergence angle and low jitter 40 GHz AlGaInAs/InP 1.55 μm mode-locked lasers

We demonstrate a novel (to the best of our knowledge) 40 GHz passively mode-locked AlGaInAs/InP 1.55 μm laser with a low divergence angle (12.7°×26.3°), timing jitter of 1.2 ps (10 kHz-100 MHz), and a radio frequency linewidth of 25 kHz.

Monolithic integration in InGaAs-InGaAsP multiquantum-well structure using laser processing

We report the use of a laser irradiation process, which combines irradiation by continuous wave and Q-switched pulsed Nd:YAG lasers, to promote quantum-well intermixing. Differential shifts up to 70 meV have been obtained in GaInAsP structures. Extended cavity-ridge lasers with 800-/spl mu/m-long active sections and 1000-/spl mu/m-long passive sections, were fabricated. The slope efficiency of the extended cavity lasers is very close to that of 800-/spl mu/m-long all-active lasers, and the threshold current is 10 mA higher than for an 800-/spl mu/m-long all-active device. The loss in the intermixed single-mode waveguide is 2.1 cm/sup -1/.

Quantum well intermixing in material systems for 1.5 μm (invited)

Precise control over local optical and electrical characteristics across a semiconductor wafer is a fundamental requirement for the fabrication of photonic integrated circuits. Quantum well intermixing is one approach, where the band gap of a quantum well structure is modified by intermixing the well and barrier layers. Here we report recent progress in the development of intermixing techniques for long wavelength applications, discussing two basic techniques. The first is a class of laser disordering techniques which take place in the solid state. The second is a novel intermixing technique involving plasma induced damage. Both techniques enable large band gap shifts to be achieved in standard GaInAsP multiple quantum well laser structures. The potential of both techniques for photonic integration is further demonstrated by the fabrication and characterisation of extended cavity lasers.

Control of multiple bandgap shifts in InGaAs-AlInGaAs multiple-quantum-well material using different thicknesses of PECVD SiO 2 protection layers

A useful development of the sputtered SiO/sub 2/ intermixing technique is reported, which uses a single stage of sputtered SiO/sub 2/ deposition and annealing to achieve precise tuning of the bandgap energy in the InGaAs-AlInGaAs material system. The blue shift of photoluminescence spectra can be varied in the range of 0-160 nm. Bandgap-tuned lasers were integrated on a single chip using this technique to assess the post-processed material characteristics and demonstrate its application in optoelectronic integration.

Monolithic 40-GHz Passively Mode-Locked AlGaInAs–InP 1.55-

We have fabricated 40-GHz passively mode-locked AlGaInAs-InP 1.55- lasers integrated with surface-etched distributed Bragg mirrors. Numerically optimized gratings provide low-scattering losses and accurate wavelength control. The lasers produce 4.46-ps Gaussian pulses with time-bandwidth product of 0.47.

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Record values for the rollover power and rollover linear power densities of 9xx nm devices, obtained by simultaneous scaling of length and d/Γ, are reported. The values for d/Γ lay in the range 0.8 μm to 1.2 μm with corresponding cavity lengths from 3.5 mm to 5 mm. The transversal structures were asymmetric, with a higher refractive index on the n side. An optical trap was helpful in reducing the radiation extension on the p side and the overall thickness. The highest rollover linear power densities were 244 mW/μm for structures without an optical trap and 290 mW/μm for those that included an optical trap