R. F. Kazarinov

Second-order distributed feedback lasers with mode selection provided by first-order radiation losses

We present a theoretical study of the effect of radiation losses on the mode selectivity of DFB lasers with second-order gratings. For a second-order grating, interference of the radiation due to first-order diffraction of oppositely propagating guided waves cancels the radiation loss at one of the edges of the spectrum gap. This provides threshold gain discrimination of order 10 cm-1against one of the two dominant modes occurring near the edges of the gap. This should allow fabrication of DFB lasers with properties that are nearly independent of the positions of the facets relative to the grating corrugations, which are uncontrolled. By applying antireflection coatings to the two ends, differential quantum efficiencies close to those of conventional Fabry-Perot lasers should be achievable.

Glass waveguides on silicon for hybrid optical packaging

Work on deposited glass waveguides on silicon to form waveguides and filters is reviewed. The choice of these particular waveguides makes sense only as part of a consistent approach to optoelectronic packaging. Hybrid optical packaging on silicon (HOPS) is described and briefly compared with other techniques. For these packages, two waveguides were developed: a tight mode waveguide with a silicon nitride rib core for matching a semiconductor laser and a loose mode waveguide with a phosphosilicate glass core for matching an optical fiber. >

Integrated four-channel Mach-Zehnder multi/demultiplexer fabricated with phosphorous doped SiO/sub 2/ waveguides on Si

An analysis and the device performance of an integrated optical 4-channel multi/demultiplexer based on Mach-Zehnder interferometers elements are presented. The channel spacing is 77 AA. Single-mode channel waveguides are made from P-doped SiO/sub 2/ core layers. Waveguide losses as low as 0.05 dB/cm and fiber-to-waveguide butt coupling as low as 0.5 dB for lambda =1.5 mu m have been obtained. The multiplexer transfers power from four input channels into a common output channel with an average fiber-to-fiber loss of 2.6 dB per channel. The average crosstalk of the demultiplexer is -16 dB. >

The relation of line narrowing and chirp reduction resulting from the coupling of a semiconductor laser to passive resonator

We present a theory of adiabatic chirp reduction and narrowing of the Lorentzian laser line that occurs when a laser is coupled to an external passive resonator. Chirp reduction and line narrowing are simply related. We show that the reduction in the Lorentzian line width is equal to the square of the reduction in adiabatic chirp. Both are strongly enhanced near resonances of the external cavity.

Low loss Si(3)N(4)-SiO(2) optical waveguides on Si.

We have developed an optical integrated circuit waveguide technology based on conventional Si processing. We demonstrate waveguide losses of <0.3 dB/cm in the 1.3-1.6-microm wavelength range. We use a high refractive-index core of Si(3)N(4) surrounded by SiO(2) cladding layers, which provides a highly confined optical mode adequate for butt coupling to channel substrate buried heterostructure lasers. We report the first IR transmission experiments in these waveguides and find two absorption peaks associated with H in SiO(2) and Si(3)N(4) layers at 1.40 and 1.52 microm, respectively. The peak absorptions are 2.2 and 1.2 dB/cm, respectively, and these peaks can be largely removed by annealing at 1100-1200 degrees C.

Four-channel wavelength division multiplexers and bandpass filters based on elliptical Bragg reflectors

Four-channel multiplexers and four-wavelength bandpass filters based on elliptical Bragg reflectors (EBRs) are discussed. The channel spacing is 50 AA near 1.56 mu m. The EBRs are narrowband elliptical mirrors that can refocus light from an input waveguide to any one of a number of output waveguides. Spectrally, they perform similarly to Bragg reflectors. The devices were fabricated on silicon using silica-based waveguide technology. The elliptical gratings with 0.53- mu m periods were patterned using deep UV spatial frequency doubling photolithography. Multiplexers with single filtering and double filtering were demonstrated. With single filtering, the fiber-to-fiber insertion loss was 3.0+or-0.5 dB, and the crosstalk was -20 dB; with double filtering, the insertion loss was 4.0+or-0.5 dB, and the crosstalk was -30 dB. About 2 dB of this loss was due to coupling between the fibers and the waveguide. The additive loss associated with the EBR, including propagation, Bragg reflection, and coupling between input and output waveguides, was about 1 dB. >

Integrated optic adiabatic devices on silicon

A study of integrated optic devices based on adiabatic principles is reported. The components are a 3-dB coupler, a full coupler, a polarization splitter, a wavelength multiplexer, and two mode shape transformers. All components were fabricated from doped silica and silicon nitride films on silicon substrates. Results are given for an adiabatic full coupler and an adiabatic 3-dB coupler, an asymmetric Y-coupler for a 1.3-1.55- mu m-wavelength multiplexer, and a tapered waveguide for mode shape transformation. >

Charge injection over triangular barriers in unipolar semiconductor structures

A theory of unipolar current over triangular barriers in semiconductor structures is developed. Diodes based on such barriers have been recently fabricated by molecular beam epitaxy using either variable‐gap or modulation‐doped semiconductors. In these diodes the current is due to unipolar injection of electrons. Exact analytic expression for current‐voltage characteristics is obtained. Comparison is made with recent experimental data.

Observation of destructive interference in the radiation loss of second-order distributed feedback lasers

We report measurements of the distribution of 90° radiation loss along the length of an optically pumped distributed feedback resonator having a second-order grating and nonreflecting ends. The loss is strong at the ends, but nearly cancels at the center due to destructive interference of the scattered radiation from the oppositely propagating waves forming the lasing mode. This is the first observation of this interference effect, which provides an important source of single mode selection in distributed feedback lasers with second-order gratings.

Carrier transport in laser heterostructures

We present two-dimensional numerical simulation of carrier transport in laser structures, which allows calculation of the efficiency of injected carrier consumption by the active region and the dependence of the laser current on applied voltage. It also allows calculation of the current, carrier, and potential distribution in a laser structure. This was done by use of PADRE, a program developed for the modeling of heterostructure electronic devices, which was supplemented with additional calculations of the laser optical properties. We applied this program to investigate the effect on the laser quantum efficiency of thermionic emission of electrons from the active layer. The temperature and current dependence of the laser internal quantum efficiency has been analyzed. This study allowed us to understand the performance of lasers with nearly ideal current-blocking structures. >