The Laser Interferometer Space Antenna (LISA), with its extreme distance measurement requirements (pm over arm lengths of 2.5 Mio km), imposes many stringent requirements on the laser sources used for interferometry. Frequency and power stability, as well as the side band phase noise represent considerable technological challenges, that must be maintained over the full 12.5 years mission duration. These constraints demand a streamlined laser design and a particular attention to reliability and procurement strategy, which poses a significant challenge. The main requirements for the laser critical sub-system have been analyzed. The Centre Suisse d’Electronique et de Microtechnique (CSEM), in the frame of a European Space Agency activity, was mandated to demonstrate a laser head for the LISA mission based on an alternative laser oscillator approach that does not rely on the LISA-baseline technology (i.e. Nd:YAG NPRO laser). The activity was named MONALISA. After a presentation of the key laser head requirements, the laser head design is described. A comprehensive test campaign was performed, and test results are presented.
We report on our efforts to develop a whispering gallery mode resonator etalon as a tool for precision radial velocity observations to detect exoplanets. The crystalline MgF2 etalon will be referenced to a compact fiber laser frequency comb, and will serve as the wavelength calibration source for a stabilized, high resolution, visible band spectrograph. The extreme stability required for the detection and characterization of exo-Earths orbiting solar-type stars will be achieved by employing a composite resonator structure with a compensating material to balance the resonator’s coefficients of thermal expansion and thermal refractivity. Progress in modeling the etalon to achieve single mode-like performance, and experiments to demonstrate broad-band (octave-spanning) ling to a white light source, are described.
Narrow-linewidth lasers operating in the near-infrared provide precise timing synchronization for atomic optical clocks and quantum computers. Crystalline ultra-high-Q optical resonators enable high-performance laser design in a small form factor that allow miniaturization of the devices using the lasers. Here we demonstrate a 780 nm self-injection-locked laser with Hertz-level instantaneous linewidth under single-mode continuous-wave operation. The self-injection locking induced by the whispering gallery mode resonator suppresses the frequency noise and reduces the drift of the free running device.
A crystalline microresonator with overall thermal sensitivity of the optical spectrum approaching zero is designed and demonstrated experimentally. The resonator is made by integrating a calcium fluoride layer forming an optical whispering gallery mode resonator with ceramic compensation layers. The ceramics is characterized with negative thermal expansion coefficient in a limited temperature range. The thermally compensated resonator has a potential application for laser frequency stabilization. We demonstrate a self-injection locked laser characterized with Allan Deviation on the order of 10^-12 at 1s integration time and study the factors limiting its stability.
NASA is working with US industry and academia to develop Photonic Integrated Circuits (PICs) for: (1) Sensors (2) Analog RF applications (3) Computing and free space communications. The PICs provide reduced size, weight, and power that is critical for space-based systems. We describe recent breakthrough 3D monolithic integration of photonic structures, particularly high-speed graphene-silicon devices on CMOS electronics to create CMOS-compatible highbandwidth transceivers for ultra-low power Terabit-scale optical communications. An integrated graphene electro-optic modulator has been demonstrated with a bandwidth of 30 GHz. Graphene microring modulators are especially attractive for dense wavelength division multiplexed (DWDM) systems. For space-based optical communication and ranging we have demonstrated generating a variable number of channels from a single laser using breadboard components, using a single-sideband carrier-suppressed (SSBCS) modulator driven by an externally-supplied RF tone (arbitrary RF frequency), a tunable optical bandpass filter, and an optical amplifier which are placed in a loop. We developed a Return--to-Zero (RZ) Differential Phase Shift Keying (DPSK) laser transmitter PIC using an InP technology platform that includes a tunable laser, a Semiconductor Optical Amplifier (SOA), high-speed Mach-Zehnder Modulator (MZM), and an electroabsorption (EAM) modulator. A Silicon Nitride (SiN) platform integrated photonic circuit suitable for a spectrally pure chip-scale tunable opto-electronic RF oscillator (OEO) that can operate as a flywheel in high precision optical clock modules, as well as radio astronomy, spectroscopy, and local oscillator in radar and communications systems is needed. We have demonstrated a low noise optical frequency combs generation from a small OEO prototypes containing very low loss (~1 dB) waveguide couplers of various shapes and sizes integrated with an ultrahigh-Q MgF2 resonators. An innovative miniaturized lab-on-a-chip device is being developed to directly monitor astronaut health during missions using ~3 drops of body fluid sample like blood, urine, and potentially other body fluids like saliva, sweat or tears. The first-generation system comprises a miniaturized biosensor based on PICs (including Vertical Cavity Surface Emitting Laser – VCSEL, photodetector and optical filters and biochemical assay that generates a fluorescent optical signal change in response to the target analyte.
We report on our recent experiments involving tight packaging of RF photonic oscillators based on optical Kerr frequency combs generated in nonlinear optical microresonators. The devices with volume not exceeding one cubic centimeter characterized with phase noise approaching -120 dBc/Hz at 10 kHz frequency offset are demonstrated at 26 GHz and 28 GHz. Possibilities of tuning the oscillators with a piezo-actuator are discussed.
We theoretically study both the technical and the fundamental quantum limitations of the sensitivity of a resonant optical gyroscope based on a high finesse optical cavity. We show that the quantum back action associated with the resonantly enhanced optical cross and self-phase modulation results in the nonlinear optics-mediated standard quantum limit (SQL) of the angle random walk of the gyroscope. We also found that the measurement sensitivity of a generic optical gyroscope is fundamentally limited due to the opto-mechanical properties of the device. Ponderomotive action of the light interrogating the gyroscope cavity leads to the opto-mechanical SQL of the rotation angle detection. The uncorrelated quantum fluctuations of power of clockwise and counterclockwise light waves result in optical power-dependent uncertainty of the angular gyroscope position.
Interband and Quantum Cascade Lasers are key sources for MIR molecular sensing. Understanding their noise features and stabilizing their emission is of fundamental importance for applications like precision spectroscopy and metrology. High-Q crystalline Whispering Gallery Mode Resonators have proven to be powerful tools for characterization and stabilization of lasers from the UV to the MIR. Here, we report our recent results on Whispering Gallery Mode Resonators used for frequency characterization, stabilization and linewidth narrowing of Interband and Quantum Cascade Lasers. These results pave the way to new classes of compact MIR sources usable in Space missions, Metrology and Fundamental Physics.
We report on a study of performance of both active and passive optical gyroscopes based on high finesse crystalline whispering gallery mode (WGM) resonators. We show that the sensitivity of the devices is ultimately limited due to the nonlinearity of the resonator host material. A gyroscope characterized with 0.02 deg/hr^1/2 angle random walk and 2 deg/hr bias drift is demonstrated.
Narrow-linewidth lasers are key elements in optical metrology and spectroscopy. From their spectral purity, the measurements accuracy and the overall quality of collected data critically depend. Crystalline micro-resonators have undergone an impressive development in the last decade, opening new ways to photonics from the mm to the μm scale. Their wide transparency range and high Q-factor make them suitable for integration in compact apparatuses for precision spectroscopy from the visible to the mid-IR. Here, we present our recent results on frequency stabilization and linewidth narrowing of quantum cascade lasers using crystalline Whispering Gallery Mode Resonators for mid-IR precision spectroscopy.
This paper presents a novel architecture for a high performance atomic clock based on the use of miniature optical whispering gallery mode (WGM) resonators. Following the approach of stabilizing a laser local oscillator to an optical transition in an atom or ion, as used in advanced atomic clock, a semiconductor laser is used for stabilization to the D1 line of Rb atoms, held in a small vapor cell. The laser is self-injection locked to a WGM resonator to reduce its linewidth. To produce the RF output of the clock, a second WGM resonator excited with a second cw semiconductor laser produces an optical frequency comb that is demodulated on a fast photodiode. Locking the resonator that generates the frequency comb to the laser stabilized to the Rb transition transfers the stability of the atomic transition to the RF output of the clock. In this way, a miniature all-optical atomic clock is realized. Details of the operation of the clock and application of the architecture to other atomic systems, such as a ytterbium ion, will be described.
We study theoretically and demonstrate experimentally generation of coherent optical frequency combs in a sapphire whispering gallery mode resonator. We verify phase locking of the comb harmonics by demodulating the comb on a fast photodiode and by observing the production of a spectrally pure radio frequency signal. Because of excellent optical and superior mechanical properties of the material, the sapphire resonator is an excellent candidate for the on-chip device integration of the comb oscillator.
We discuss our recent progress in iimproving the phase noise of a semiconductor laser using self-injection locking of to a mode of a high-Q whispering gallery mode resonator. Locking efficiency is analyzed for semiconductor distributed feedback (DFB) as well as Fabry-Perot (FP) lasers operating at 690 nm, 1060 nm, 1550 nm, and 2 μm. Instantaneous linewidth below 300 Hz is realized with telecom DFB lasers. Tunability of the lasers is demonstrated. Commercially available packaged ”plug-and-play” devices are manufactured.
Different applications of crystalline whispering gallery mode resonators call for different properties of the resonator host material. We report on our recent study of resonators made out of sapphire, diamond, and quartz crystals and discuss possible applications of these resonators. In particular, we demonstrate Kerr frequency comb generation in sapphire microresonators.
It is well known that light is able to modify properties of solid state media. Photorefractivity is one of the brightest
demonstrations of such an ability. The phenomenon is related to the change of refractive index resulting from light-mediated redistribution of charges within the material.1 This redistribution is particularly pronounced in a selected class of optical materials. The magnitude of photorefractivity depends on the energy of photons that induce the charge redistribution, and thus is generally not observed with infrared light. In this work we demonstrate experimentally that not only light, but also low power radio-frequency (RF) electromagnetic radiation results in a significant modification of the refractive index of strontium barium niobate (SBN), one of the widely used photorefractive material. To our knowledge, the observed effect cannot be explained using existing theories of photorefractivity in bulk material. We expect that the effect originates from the influence of the boundary of the material on the space charge distribution as well as RF field induced pyroelectric effect; however a more detailed study is required to completely unveil the origin of the phenomenon.
We investigate opto-mechanical oscillation (OMO) and subsequent generation of acoustic wave frequency combs
in monolithic crystalline whispering gallery mode (WGM) resonators. The OMO is observed in resonators made
of electro-optic (lithium tantalate), non-electro-optic birefringent (magnesium fluoride), and non-birefringent
(calcium fluoride) materials. The phenomenon manifests itself as generation of optical harmonics separated by
the eigenfrequency of a surface acoustic wave (SAW) mechanical mode of the same WGM resonator. We show
that the light escaping the resonator and demodulated on a fast photodiode produces a spectrally pure radio
frequency (RF) signal. For instance, we demonstrate generation of 200 MHz signals with instantaneous linewidth
of 0.2 Hz.
We investigate several possibilities of designing spectrum of a whispering gallery mode resonators to create
groups of optical modes with desired free spectral range as well as group velocity dispersion. This will enable
efficient resonant nonlinear frequency conversion processes such as hyper-parametric and parametric oscillations,
frequency doubling, and electro-optical frequency shifting and modulation. We show that the spectral design
can be achieved via a proper modification of the shape of the resonator and via the change of the distribution of
the refractive index of the resonator host material.
We report on the realization of a compact-package (44x27x14mm) narrow linewidth laser based on self-injection
locking of a distributed feedback semiconductor diode laser to a high-Q whispering gallery mode resonator
fabricated with electro-optic material. The packaged device operates at 1,550 nm and offers instantaneous
spectral linewidth performance smaller than 1.8 kHz for 3 mW of output power. We are able to tune the laser
frequency by applying voltage to the resonator. This suggest that the technology enables fabrication of ultra
narrow linewidth semiconductor lasers in a broad wavelength range of 390 nm to 2,900 nm. The laser source in a
compact footprint enables a multitude of sensing, monitoring, and metrology applications where high resolution
and precision and absolute accuracy are required.
We propose theoretically and demonstrate experimentally a method for generation of beams of light possessing
large angular momenta. The method utilizes cylindrical optical waveguides as well as whispering gallery mode
resonators that efficiently transform a plane electromagnetic wave into truncated Bessel beams. Generation of
the high order beams with well defined angular momenta is demonstrated.
We introduce a definition of group velocity for a system with a discreet spectrum and apply it to a linear
resonator. We show that a positive, negative, or zero group velocity can be obtained for light propagating in the
whispering gallery modes of a microspherical resonator. The associated group delay is practically independent
of the ring-down time of the resonator. We demonstrate "stopped light" in an experiment with a fused silica
microsphere.
We theoretically study propagation of light in a vertically coupled whispering gallery mode resonator (WGMR) waveguide consisting of a chain of disc WGMRs etched on the surface of a cylinder made of an optically transparent material. The waveguide is capable of reducing the group velocity of light by as much as a factor of a billion, is much more efficient than usual coupled resonator optical waveguides, and compete with slow light atomic systems. We discuss practical as well as fundamental advantages and disadvantages of the resonator and atomic delay lines.
By engineering the geometry of a nonlinear optical crystal, the effective efficiency of all nonlinear optical oscillations can be increased dramatically. Specifically, sphere and disk shaped crystal resonators have been used to demonstrate nonlinear optical oscillations at sub-miliwatt input power when cw light propagates in a Whispering Gallery Mode (WGM) of such a resonant cavity. In terms of both device production and experimentation in quantum optics, some nonlinear optical effects with naturally high efficiency can occult the desired nonlinear scattering process. The efficiency of second order nonlinear optical effects in ferroelectric crystals can be increased by engineering a poling structure to the crystal resonator. In this paper, I will discuss a new method for generating poling structures in ferroelectric crystal resonators called calligraphic poling. The details of the poling apparatus, experimental results, and speculation on future applications will be discussed.
We report on observation of photorefractive effects in whispering
gallery mode resonators made of as-grown lithium niobate and lithium
tantalate in the near as well as far infrared. The effects manifested themselves as dynamic modification of the spectra as well
as quality factors of the resonators coupled to the laser radiation.
We report on fabrication of new ultrahigh Q crystalline microcavities. Optical Q factor of (4.4±1.2)×108 is achieved for Vacuum UV grade CaF2 cavity with 100 μm in diameter. It is shown that if excimer grade crystal is used, Q factor of 5.5 mm cavity can be as high as (5.31±0.04)×1010 at laser wavelength of 1064 nm. We discuss nonlinear properties of these cavities such as Raman lasing with threshold of less than a few microwatts. Possible application in cavity quantum electrodynamics is analyzed.
We theoretically show that achieving high Q-factors of small
whispering gallery mode resonators, together with significant
non-harmonism (non-equidistance) of its modes, allows for
extensive analogy between properties of atoms and the resonator
modes. The non-harmonism in very high-Q microresonators is caused
by the material as well as geometrical dispersion. The established
analogy leads to creating of a "photonic" media with properties
similar to those of atomic media. For instance, effective
"two-level" systems can be formed within the resonator. The
"levels" of the systems, i.e. the resonator modes, can be coupled
with microwave or optical fields. Strong confinement of the light
in the resonator along with high Q-factors results in nonlinear
processes at low light levels even with small nonlinearities
typical of optically transparent materials.
We present a study of optical hyper-parametric oscillator based on
a nonlinear high-Q whispering gallery mode resonator and
demonstrate that the oscillator produces stable narrow band beat
note of the pump, signal, and idler waves making an all-optical
secondary frequency reference feasible. We discuss possibilities
of tuning of the oscillator.
We demonstrate tunable optical filters fabricated from metalized
lithium niobate disk resonators and discuss further applications
of the resonator chains for tunable photonic delay lines.
We report on our recent results concerning fabrication of high-Q whispering gallery mode (WGM) crystalline resonators, and discuss some possible applications of lithium niobate WGM resonators in nonlinear optics and photonics. In particular, we demonstrate experimentally a tunable third-order optical filter-fabricated from the three metalized resonators; and report observation of parametric frequency doubling in a WGM resonator made of periodically poled lithium niobate (PPLN).
We review various photonics applications of whispering gallery
mode (WGM) dielectric resonators and focus on the capability of
generating trains of short optical pulses using WGM lithium
niobate cavities. We introduce schemes of optical frequency comb
generators, actively mode-locked lasers, and coupled
opto-electronic oscillators where WGM cavities are utilized for
the light amplification and modulation.
We demonstrate novel techniques to manipulate spectral properties
of high quality factor whispering-gallery modes (WGM) in optical dielectric microresonators. These include permanent frequency trimming of WGM frequencies by means of UV photosensitivity of germanium doped silica resonators; electro-optical tuning of WGM in lithium niobate resonators, and cascading of microresonators for obtaining second-order filtering function. We present theoretical interpretation of experimental results, and examples of applications of these techniques for photonic microwave filtering.
We propose to fabricate a dielectric cavity sustaining high-Q whispering gallery modes from a periodically poled material possessing a quadratic nonlinearity to achieve an efficient interaction among the modes. We show that the periodical poling allows for compensation of both the material and the cavity dispersions that prohibits the nonlinear interaction otherwise. Such a cavity might be a basic element of a family of efficient nonlinear devices operating at a broad range of optical wavelengths.
We present electro-optic modulator based on toroidal lithium niobate cavity with whispering-gallery modes, superimposed with stripline resonator. With microwave resonance (quality-factor Q ~ 102) tuned to the free spectral range of optical modes (Q ~ 5x106), controlling power ú10mW is achieved in 9GHz prototype, and preliminary results with 33GHz prototype are obtained. Further efficiency improvement will enable various applications in microwave photonics.
A general model is presented for coupling of high-Q whispering-gallery modes in optical microsphere resonators with coupler devices possessing discrete and continuous spectrum of propagating modes. By contrast to Fabry-Perot resonators, in microspheres independent high intrinsic quality-factor and controllable parameters of coupling via evanescent field offer variety of regimes earlier available in RF devices. Latest results on realization of material- limited Q approximately 1010 in microspheres in the visible and near-infrared band and preservation of very-high Q in surface-hydration-preventing environment are presented.
We demonstrate the quality factor Q equals (0.8 plus or minus 0.1) multiplied by 1010 of whispering-gallery modes in fused silica microspheres at 633 nm, close to the limit determined by fundamental material attenuation. The lifetime of ultimate Q is limited by adsorption of atmospheric water. Optical effects of adsorption are investigated and conditions for fabrication of long-lifetime microspheres are clarified.
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