A new time-domain Fourier-Galerkin (TDFG) theory is developed to simulate the near-field, far-field and spectral characteristics of surface-emitting photonic-crystal distributed-feedback (SE PCDFB) lasers. It is found that a properly-designed two-dimensional hexagonal or square-lattice grating should efficiently couple the output into a single SE mode that retains coherence for aperture diameters of up to /spl ap/1 mm. We identify lattice structures and precise conditions under which all components of the transverse electric or transverse magnetic polarized optical fields constructively interfere to produce a single-lobed, near-diffraction-limited circular output beam. The TDFG simulations predict that quantum efficiencies as high as 30% (60% if reflectors are built into the waveguide structure) should be attainable. A surprising conclusion is that diffractive coupling into the surface-emitting direction must be relatively weak, in order to assure selection of the desired symmetric in-phase mode. Furthermore, gain media with a moderate linewidth enhancement factor should produce the best SE PCDFB performance, whereas edge emitters nearly always benefit from a very small value.

Design optimization for high-brightness surface-emitting photonic-crystal distributed-feedback lasers

Because of an intrinsically low linewidth-enhancement factor, the quantum cascade laser (QCL) is especially favorable for patterning with a recently proposed 2-D photonic crystal (PC) lattice that substantially increases the device area over which optical coherence can be maintained. In this work, we use an original time-domain Fourier-transform (TDFT) algorithm to theoretically investigate the beam quality and spectral purity of gain-guided PC distributed-feedback (DFB) quantum cascade lasers. The conventional 1-D DFB laser and also the angled-grating DFB (/spl alpha/-DFB) laser are special cases of the PCDFB geometry. By searching the parameter space consisting of tilt angle, coupling coefficients, stripe width, and cavity length, we have theoretically optimized the PCDFB gratings for QCL gain regions. At a wavelength of 4.6 /spl mu/m, the simulations project single-mode emission from stripes as wide as 1.2 mm, and etendues of no more than three times the diffraction limit for 2-mm stripes. We also examine the tolerances required for single-mode and high-brightness operation. Comparisons are made to analogous simulations of a-DFB QCL lasers.

Photonic-crystal distributed-feedback quantum cascade lasers

A multimode interference device and method of making the same comprises at least one input port, at least one output port, a multimode interference region separating the input port from the output port, and at least one subregion in the multimode interference region, wherein a self-image length within the multimode interference region is reduced by a factor that is approximately equal to one plus a number of subregions configured in the multimode interference region, wherein the at least one subregion is configured to have an effective width and effective refractive index running longitudinally through the multimode interference region. Additionally, the subregion may comprise at least one slot.

Slotted multimode interference device

A photonic-crystal distributed-feedback laser includes a laser cavity with a waveguide structure that has a cavity length Lc and is bounded by two mirrors (146; 148); an active region (150) for producing optical gain upon receiving optical pumping or an input voltage; at least one layer (156) having a periodic two-dimensional grating with modulation of a modal refractive index, the grating being defined on a rectangular lattice with a first period along a first axis of the grating and a second period along a second perpendicular axis of the grating, and wherein the grating produces three diffraction processes having coupling coefficients K1, K2 K3 and a lateral gain area contained within a second area patterned with the grating that has substantially a shape of a gain stripe with a width W, with the gain stripe tilted at a first tilt angle relative to the two mirrors (146; 148). The rectangular lattice of the grating is tilted at a second tilt angle substantially the same as the first tilt angle with respect to the gain stripe, and the ratio of the first and second grating periods is equal to the tangent of the first tilt angle, with the first tilt angle being between about 16° and about 23°.

Photonic-crystal distributed-feedback and distributed-bragg reflector lasers

Electron-beam lithography was used to pattern a second-order photonic-crystal distributed feedback grating onto an antimonide type-II "W" laser emitting at /spl lambda//spl ap/3.7 /spl mu/m. For pulsed optical pumping, the output beam was essentially diffraction-limited up to a stripe width of 150 /spl mu/m, and remained no worse than eight times the diffraction limit for stripes as wide as 600 /spl mu/m. This represents a considerable improvement over all previous mid-infrared semiconductor lasers with such broad stripes.

Broad-stripe near-diffraction-limited mid-infrared laser with a second-order photonic-crystal distributed feedback grating

Theoretical modeling of InP coupled-quantum-well electroabsorptive and electrorefractive modulators is presented. Key mathematical transformations are developed that allow efficient computation of electrorefraction for a complex multiparameter coupled quantum well structure. The model is realized in the Mathematica platform and is used to simulate the impact of well and barrier composition and thickness on Mach-Zehnder modulator performance. The advantage of using coupling between quantum wells is quantified and in addition, it is shown that linewidth broadening is a key input to the model and has a critical impact on modulator performance. The model is compared to experimental data from phase modulators and Mach-Zehnder intensity modulators.

Electrorefractive Coupled Quantum Well Modulators: Model and Experimental Results

We demonstrate single mode operation of laser diode cavities up to 200|iim wide using 2-D Bragg gratings for simultaneous longitudinal and lateral mode control.

Large spatial mode, single frequency semiconductor lasers using two dimensionalgratings

In this work, multimode interference in a semiconductor optical amplifier is used to simultaneously split (× 10) and amplify a RF signal on an optical carrier.

Analog Signal Splitting and Amplification for Optically-Controlled Phased-Array Antennas

Experimental and analytical results for semiconductor electro-refractive modulators will be presented. Modulation structures investigated include quantum wells, coupled quantum wells and quantum dots.

Semiconductor electrorefractive modulators

A RF spectrum analyzer with high performance and unique capabilities that traditional all-electronic spectrum analyzers
do not exhibit is demonstrated. The system is based on photonic signal processing techniques that have enabled us to
demonstrate the spectral analysis of a 1.5 GHz bandwidth with a 1.4 ms update time and a resolution bandwidth of 31
kHz. We observed a 100% probability of intercept for all signals, including short pulses, during the measurement
window. The spectrum analyzer operated over the 0.5 to 2.0 GHz range and exhibited a spur-free dynamic range of 42
dB. The potential applications of such a system are extensive and include: detection and location of transient electromagnetic
signals, spectrum monitoring for adaptive communications such as spectrum-sensing cognitive radio, and
battlefield spectrum management.

Larry Lembo

Papers

Electrorefractive Coupled Quantum Well Modulators: Model and Experimental Results

Large spatial mode, single frequency semiconductor lasers using two dimensionalgratings

Analog Signal Splitting and Amplification for Optically-Controlled Phased-Array Antennas

Semiconductor electrorefractive modulators

Photonically enabled RF spectrum analyzer demonstration