Squeezed-light generation in a nonlinear planar waveguide with a periodic corrugation

Two-mode nonlinear interaction (second-harmonic and second-subharmonic generation) in a planar waveguide with a small periodic corrugation at the surface is studied. Scattering of the interacting fields on the corrugation leads to constructive interference that enhances the nonlinear process provided that all the interactions are phase matched. Conditions for the overall phase matching are found. Compared with a perfectly quasi-phase-matched waveguide, better values of squeezing as well as higher intensities are reached under these conditions. Procedure for finding optimum values of parameters for squeezed-light generation is described.Comment: 14 pages, 14 figure

Ultra-low threshold CW Triply Resonant OPO in the near infrared using Periodically Poled Lithium Niobate

We have operated a CW triply resonant OPO using a PPLN crystal pumped by a Nd:YAG laser at 1.06 micron and generating signal and idler modes in the 2-2.3 micron range. The OPO was operated stably in single mode operation over large periods of time with a pump threshold as low as 500 microwatts.Comment: 7 pages, 5 figures, submitted to JEOS

Fabrication, Packaging, and Performance of VCSELs and Photodetectors for Space Applications

Optocouplers are used for a variety of applications aboard spacecraft including electrical isolation, switching and power transfer. Commercially available light emitting diode (LED)-based optocouplers have experienced severe degradation of light output due to extensive displacement damage occurring in the semiconductor lattice caused by energetic proton bombardment. A new optocoupler has been designed and fabricated which utilizes vertical cavity surface emitting laser (VCSEL) and resonant cavity photodetector (RCPD) technologies for the optocoupler emitter and detector, respectively. Linear arrays of selectively oxidized GaAs/AlGaAs VCSELS and RCPDS, each designed to operate at a wavelength of 850nm, were fabricated using an airbridge contacting scheme. The airbridged contacts were designed to improve packaging yields and device reliability by eliminating the use of a polyimide planarizing layer which provided poor adhesion to the bond pad metallization. Details of the airbridged optocoupler fabrication process are reported. Discrete VCSEL and RCPD devices were characterized at temperatures between {minus}100 to 100 C. Devices were packaged in a face-to-face configuration to form a single channel optocoupler and its performance was evaluated under conditions of high-energy proton bombardment

Two-element phased array of antiguided vertical-cavity lasers

We demonstrate for the first time anti-guided coupling of two adjacent vertical-cavity surface-emitting lasers (VCSEL's), obtaining a 1-by-2 phase-locked array at 869 nm. The lateral index modification required for anti-guiding is achieved by a patterned 3-rim etch performed between two epitaxial growths. In contrast with prior evanescently coupled VCSEL's, adjacent anti-guided VCSEL's can emit in-phase and produce a single on-axis lobe in the far field. Greater than 2 mW of in-phase output power is demonstrated with two VCSEL's separated by 8 {micro}m. Moreover, phase locking of two VCSEL's separated by 20 {micro}m is observed, indicating the possibility of a new class of optical circuits based upon VCSEL's that interact horizontally and emit vertically

Pulsed quadrature-phase squeezing of solitary waves in chi((2)) parametric waveguides

It is shown that coherent quantum simultons (simultaneous solitary waves at two different frequencies) can undergo quadrature-phase squeezing as they propagate through a dispersive chi((2)) waveguide. This requires a treatment of the coupled quantized fields including a quantized depleted pump field. A technique involving nonlinear stochastic parabolic partial differential equations using a nondiagonal coherent state representation in combination with an exact Wigner representation on a reduced phase space is outlined. We explicitly demonstrate that group-velocity matched chi((2)) waveguides which exhibit collinear propagation can produce quadrature-phase squeezed simultons. Quasi-phase-matched KTP waveguides, even with their large group-velocity mismatch between fundamental and second harmonic at 425 nm, can produce 3 dB squeezed bright pulses at 850 nm in the large phase-mismatch regime. This can be improved to more than 6 dB by using group-velocity matched waveguides

Final report on LDRD project : single-photon-sensitive imaging detector arrays at 1600 nm.

The key need that this project has addressed is a short-wave infrared light detector for ranging (LIDAR) imaging at temperatures greater than 100K, as desired by nonproliferation and work for other customers. Several novel device structures to improve avalanche photodiodes (APDs) were fabricated to achieve the desired APD performance. A primary challenge to achieving high sensitivity APDs at 1550 nm is that the small band-gap materials (e.g., InGaAs or Ge) necessary to detect low-energy photons exhibit higher dark counts and higher multiplication noise compared to materials like silicon. To overcome these historical problems APDs were designed and fabricated using separate absorption and multiplication (SAM) regions. The absorption regions used (InGaAs or Ge) to leverage these materials 1550 nm sensitivity. Geiger mode detection was chosen to circumvent gain noise issues in the III-V and Ge multiplication regions, while a novel Ge/Si device was built to examine the utility of transferring photoelectrons in a silicon multiplication region. Silicon is known to have very good analog and GM multiplication properties. The proposed devices represented a high-risk for high-reward approach. Therefore one primary goal of this work was to experimentally resolve uncertainty about the novel APD structures. This work specifically examined three different designs. An InGaAs/InAlAs Geiger mode (GM) structure was proposed for the superior multiplication properties of the InAlAs. The hypothesis to be tested in this structure was whether InAlAs really presented an advantage in GM. A Ge/Si SAM was proposed representing the best possible multiplication material (i.e., silicon), however, significant uncertainty existed about both the Ge material quality and the ability to transfer photoelectrons across the Ge/Si interface. Finally a third pure germanium GM structure was proposed because bulk germanium has been reported to have better dark count properties. However, significant uncertainty existed about the quantum efficiency at 1550 nm the necessary operating temperature. This project has resulted in several conclusions after fabrication and measurement of the proposed structures. We have successfully demonstrated the Ge/Si proof-of-concept in producing high analog gain in a silicon region while absorbing in a Ge region. This has included significant Ge processing infrastructure development at Sandia. However, sensitivity is limited at low temperatures due to high dark currents that we ascribe to tunneling. This leaves remaining uncertainty about whether this structure can achieve the desired performance with further development. GM detection in InGaAs/InAlAs, Ge/Si, Si and pure Ge devices fabricated at Sandia was shown to overcome gain noise challenges, which represents critical learning that will enable Sandia to respond to future single photon detection needs. However, challenges to the operation of these devices in GM remain. The InAlAs multiplication region was not found to be significantly superior to current InP regions for GM, however, improved multiplication region design of InGaAs/InP APDs has been highlighted. For Ge GM detectors it still remains unclear whether an optimal trade-off of parameters can achieve the necessary sensitivity at 1550 nm. To further examine these remaining questions, as well as other application spaces for these technologies, funding for an Intelligence Community post-doc was awarded this year

Amplitude squeezing by means of quasi-phase-matched second-harmonic generation in a lithium niobate waveguide,’’

We demonstrate that traveling-wave second-harmonic generation produces amplitude-squeezed light at both the fundamental and the harmonic frequencies. Quasi-phase-matched second-harmonic conversion efficiencies approaching 60% were obtained in a 26-mm-long single-mode LiNbO 3 waveguide with pulses from a modelocked laser at 1.53 mm. The amplitude noise of the transmitted fundamental field was measured to be 0.8 dB below the shot-noise level, and the generated 0.765-mm harmonic light was measured to be amplitude squeezed by 0.35 dB. The conversion-efficiency dependence of the observed squeezing at both wavelengths agrees with theoretical predictions. Waveguide losses appear to degrade the squeezing, but the maximum observed squeezing is currently limited only by the available input power

Modal frequencies of vertical-cavity lasers determined by an effective-index model

Previously, an effective index optical model was introduced for the analysis of lateral waveguiding effects in vertical-cavity surface-emitting lasers. The authors show that the resultant transverse equation is almost identical to the one typically obtained in the analysis of dielectric waveguide problems, such as a step-index optical fiber. The solution to the transverse equation yields the lateral dependence of the optical field and, as is recognized in this paper, the discrete frequencies of the microcavity modes. As an example, they apply this technique to the analysis of vertical-cavity lasers that contain thin-oxide apertures. The model intuitively explains the experimental data and makes quantitative predictions in good agreement with a highly accurate numerical model

Two-Element Phased Array of Anti-Guided Vertical-Cavity Lasers

We demonstrate for the first time anti-guided coupling of two adjacent vertical-cavity surface-emitting lasers (VCSEL's), obtaining a 1-by-2 phase-locked array at 869 nm. The lateral index modification required for anti-guiding is achieved by a patterned 3-rim etch performed between two epitaxial growths. In contrast with prior evanescently coupled VCSEL's, adjacent anti-guided VCSEL's can emit in-phase and produce a single on-axis lobe in the far field. Greater than 2 mW of in-phase output power is demonstrated with two VCSEL's separated by 8 {micro}m. Moreover, phase locking of two VCSEL's separated by 20 {micro}m is observed, indicating the possibility of a new class of optical circuits based upon VCSEL's that interact horizontally and emit vertically

Effective Index Model Predicts Modal Frequencies of Vertical-Cavity Lasers

Previously, an effective index optical model was introduced for the analysis of lateral waveguiding effects in vertical-cavity surface-emitting lasers. The authors show that the resultant transverse equation is almost identical to the one typically obtained in the analysis of dielectric waveguide problems, such as a step-index optical fiber. The solution to the transverse equation yields the lateral dependence of the optical field and, as is recognized in this paper, the discrete frequencies of the microcavity modes. As an example, they apply this technique to the analysis of vertical-cavity lasers that contain thin-oxide apertures. The model intuitively explains the experimental data and makes quantitative predictions in good agreement with a highly accurate numerical model