T. Y. Chang

Learn More
We demonstrated for the first time above room temperature (RT) GaSb-based mid-infrared photonic crystal surface emitting lasers (PCSELs). The lasers, under optical pumping, emitted at λ(lasing)~2.3μm, had a temperature insensitive line width of 0.3nm, and a threshold power density (P(th)) ~0.3KW/cm2 at RT. Type-I InGaAsSb quantum wells were used as the(More)
We write and read a refractive-index grating in a photorefractive crystal BaTiO(3) with a single 20-nsec laser pulse at 532 nm. The grating formed is erasable with similar pulses. Diffraction efficiency decreases exponentially with the cumulative erasing light energy for 20-nsec pulses at intensity levels of 5-30 MW/cm(2). Optical energies required to write(More)
We show that it is possible to obtain 2 x 2 waveguide couplers with new power splitting ratios for cross coupling of 7%, 64%, 80% and 93% by cascading two short MMI sections. These couplers have simple geometry and low loss. They offer valuable new possibilities for designing waveguide power taps, high-Q ring resonators, ladder-structure optical filters,(More)
We demonstrate optical-beam phase conjugation by the process of two-beam coupling in photorefractive barium titanate. The incident, image-bearing beam causes exponential gain for counterpropagating waves, which are fed by noise and emerge with a power of the order of 10% of the incident beam and phase conjugate to it. This is expected from the calculated(More)
A method of cleaning up the spatial mode of a pulsed laser beam without using a pinhole is proposed and demonstrated. The method consists of performing mutually pumped phase conjugation (MPPC) between the pulsed laser beam and a cw reference, thereby transferring the desirable spatial mode of the cw beam onto the pulsed beam. In these experiments MPPC is(More)
Resonance phenomenon in general allows large responses from small inputs. This effective amplification effect has been in successful use in diverse range of sensing applications. More specifically, in case of optical resonances, various micro- and nano-resonator designs have been proposed so far with a large range of performance parameters. On the one hand,(More)
Ultrashort-cavity, thin-film lasers from In(1-x)Ga(x)As(y)P(1-y) of five different compositions, including InP and In(0.53)Ga(0.47)As, have been made to lase between 0.83 and 1.59 microm. The multitude of lasing wavelengths observed had line-to-line separations of less than 10 nm. The lasers were pumped with 1-psec pulses from a mode-locked dye laser. An(More)
In this paper, two different micron-scale negative refraction index metamaterials with fine flexibility are proposed. The proposed metamaterials are composed of “Quasi-S” structure and “H” structure respectively. Different from conventional metamaterials, the designs proposed in this paper apply to perpendicular incident waves.(More)