Active modelocking of multiple polariton lasers mediated by real time sensing offers novel capabilities for
optically based sensing. We outline a strategy based in part on short range polariton-polariton interactions
and in part on an actively managed external optical field coherent with each of the individual polariton lasers.
This actively managed coherent optical field is required to establish long range coherence between multiple
spatially distinct polariton lasers. Polariton lasers offer nonlinear behavior at excitation levels of a few quanta
of the optical field, time constants of picoseconds or less, and optical wavelength dimensions of individual
lasers. Achievement of useful long range, hundreds of meters, polariton based optical sensing appears
useful, but to require active cohering of arrays of polariton lasers. Continuous metrology and active control of
the system coherence offer unique opportunities for sensing approaching quantum limited operation. We
consider strategies and capabilities of sensing systems based on such arrays of spatially distinct, but
collectively coherent, polariton lasers. Significant advances in a number of technical areas over decades
appear needed to achieve such systems.
We describe a multilayered dielectric stack configuration designed specifically for use as a transmissive phase modulator for broadband optical signals. Applications for this device range from full aperture wavefront correction to nonmechanical beam steering arrays for free space optical communication links. Our implementation employs alternating GaAs and AlAs layers of varying thickness on a GaAs substrate to create a bandpass region of high average transmission in the near infrared. Within this transmission bandpass, the phase component of the complex transmission coefficient varies in a near-linear fashion with respect to wavelength. The transmission bandpass is designed to have a bandwidth of 21.0 nm (or 6.3THz frequency bandwidth) and to have an edge-to-edge relative phase change of greater than 4p radians. Modification of the stack materials' optical properties causes the transmission profile to shift spectrally, resulting in a phase modulation for specific bands of transmitted frequencies. Our broadband phase modulator imparts nearly a full-cycle of phase modulation with low loss and low group velocity dispersion. A sample comprising 91 alternating layers has been fabricated to exhibit the bandpass properties required for optical signal phase modulation. We experimentally characterize the sample using an interferometer and spectrometer to measure the spectral transmission and relative phase profiles and to assess the relative phase modulation in response to a variable angle of incidence. We compare the experimental data to computational predictions and discuss the results.
We present an optical delay line structure incorporating InxGa1-xAs quantum wells in the GaAs quarter- wave layers of a GaAs/AlAs distributed Bragg reflector. Applying an electric field across the quantum wells shifts and broadens the e1-hh1 exciton peak via the quantum- confined Stark effect. Resultant changes in the index of refraction thereby provide a means for altering the group delay of an incident laser pulse. Theoretical results predict tunable delays on the order of 50 fs for a 30-period structure incorporating 3 quantum wells per GaAs layer. Structure design, growth and fabrication are detailed. Preliminary group delay measurements on large-area samples with no applied bias are presented.
We describe a design for an agile, electronically- configurable, optical beam steering array to be used in directional free-space transmission of optical signals. The proposed device employs a 1D array of tunable resonant transmissive modulators constructed from customized multi- layered stacks of dielectric materials. Each modulator may be individually configured to transmit an optical signal with a known amount of phase and group velocity modulation. Proper configuration of each individual modulator results in diffractive interactions between multiple modulator outputs, providing a method for directional optical signal transmission. Of particular focus within this paper is the design of the individual modulator. We generate custom transmission functions by varying the parameters describing the modulator's specific construction, such as number of layers within the multi-layer stack, refractive indices of stack materials, layer thickness, and combinations of periodic versus non-periodic layer repetitions. A computational optimization of the variables describing the stack's construction strives to maximize the amount of optical signal modulation obtainable within defined limits. Our optimization is based largely on maximizing transmitted phase delay. We discuss trade-offs between methods of increasing device performance versus practical limitations of fabrication technologies.
We explore the physics of excitations of a small number of quanta in microresonators. In particular, we examine this physics as it relates to the dynamics of nonlinearly coupled microlaser oscillators used to generate time resolved coherent optical wavefronts. We seek wave fronts that can be both stabilized and also rapidly reconfigured by purely electro-optic means. Novel opportunities are offered by reductions in the number of quanta needed for laser, or laser-like action; advances in microcavity nonlinear optics; densely packed arrays of microlasers; adjustable micro- optical delay lines; synchronization of pulse envelopes in physically distinct lasers; and locking of optical fields in physically distinct lasers. Quantum statistical issues could become important, but are not emphasized here. Strategies for realizing an optical analog of high repetition rate agile microwave phased array radar with true delay are examined.
We have constructed a harmonically modelocked laser that includes an electronically driven modulator and an intracavity Fabry-Perot etalon. We use experimentally observed performance of this laser, and number simulations based on the operating parameters of this laser, to examine strategies for generating stable synchronized trains of ultrashort duration solitons at multi-GHz repetition rates. Introduction of a saturable absorber based on a mechanism that both saturates and recovers promptly is examined. This strategy provides means of generating stable trains of solitons, where the soliton durations are of the order of a few ps or less, as well as synchronizing those trains with optical pulsewidth precision. We identify a rapidly saturating and rapidly recovering saturable absorber with a shorter pathlength as a potentially useful improvement on the nonlinear loop mirror. Significant work remains, but generation and distribution of these synchronized ultrashort duration soliton trains over networks on a scale of km or more appear feasible.
Dynamic arrays of nonlinearly coupled mode-locked laser oscillators offer a means of generating arrays of ultrashort optical pulses where the arrays are both susceptible to rapid reconfiguration in response to small externally introduced electronic signals and yet also stable against random perturbations. We examine one specific example where the pulses in the array can be approximated as lowest order, weakly coupled solitons, propagating on multicore optical fiber.
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