Transmission Of Cavity Research Articles

Enhanced stimulated Brillouin scattering utilizing Raman conversion in diamond

Cascaded Brillouin lasers based on guided-wave structures are applied across a range of important fields such as optical communications, microwave photonics, and sensing. However, restricted by the volume and available transmission range of the gain medium, the power output and wavelength diversity of guided-wave Brillouin devices are somewhat limited. In this work, we report the design and development of a cascaded Brillouin laser based utilizing a free-space optical layout with a diamond crystal as the Brillouin gain medium. A quasi-continuous-wave, 1 μm laser was used as the pump laser, and Raman wavelength conversion is used as an intermediate process to facilitate stimulated Brillouin scattering with a low threshold. When the output transmission of the diamond cavity is 0.37% and the incident pump power is 220 W, cascading of the Brillouin–Stokes field to the eighth Stokes and the seventh anti-Stokes orders was observed. By adjusting the cavity length, the order of the cascaded Brillouin laser output is controlled. A comprehensive analysis of the Brillouin generation process and the cascade of Stokes orders is undertaken for different incident pump powers and cavity lengths. This work is expected to enable practical applications of high-power Brillouin lasers and Brillouin frequency combs.

Quantum Backaction Cancellation in the Audio Band

We report on the cancellation of quantum back action noise in an optomechanical cavity. We perform two measurements of the displacement of the microresonator, one in reflection of the cavity, and one in transmission of the cavity. We show that measuring the amplitude quadrature of the light in transmission of the optomechanical cavity allows us to cancel the back action noise between 1 kHz and 50 kHz, and obtain a more sensitive measurement of the microresonator's position. To confirm that the back action is eliminated, we measure the noise in the transmission signal as a function of circulating power. By splitting the transmitted light onto two photodetectors and cross correlating the two signals, we remove the contributon from shot noise and measure a quantum noise free thermal noise spectrum. Eliminating the effects of back action in this frequency regime is an important demonstration of a technique that could be used to mitigate the effects of back action in interferometric gravitational wave detectors such as Advanced LIGO.

Characterization of Low Loss Waveguides Using Bragg Gratings

A novel approach is developed for measuring small losses in highly transparent Si3N4/SiO 2 waveguides on a silicon chip. The approach is particularly applicable to waveguides written by high-resolution patterning techniques, such as e-beam lithography, whose lengths cannot be easily increased beyond several centimeters. This method is based on measuring the transmission of an optical cavity formed by two highly reflective ( R at least 0.999) simple Bragg gratings and a uniform waveguide between the two gratings whose length can be varied to increase the loss fitting accuracy. A theoretical model based on an ABCD matrix method is developed and used for the final loss value fitting. Experimentally, a cavity with extinction ratio over –70 dB and quality factor Q = 1.02×106 is realized. The fitting results show a waveguide loss of 0.24 ± 0.01 dB/cm and a grating loss of 0.31 ± 0.01 dB/cm. These results are obtained with relatively high index contrast ( Δn > 0.001) gratings with 0.1-pm wavelength scanning resolution. It is expected that with better design and wavelength scanning technique, this approach is applicable more generally to measure waveguide loss coefficients as low as 0.001 dB/cm.

A Q-switched Ho:YAG laser with double anti-misalignment corner cubes pumped by a diode-pumped Tm:YLF laser

We report the acousto-optically Q-switched Ho:YAG laser with double anti-misalignment corner cubes pumped by a diode-pumped Tm:YLF laser. In the continuous-wave operation of Ho:YAG laser, the maximum s-polarized output power of 3.2 W at 2090.3 nm was obtained under the absorbed pump power of 12.9 W by rotating the fast axis of quarter-wave plate to change the output transmission of laser cavity. The corresponding optical-to-optical conversion efficiency was 24.8% and the slope efficiency was 55.7%. When one of the corner cubes was rotated to 11.8° around vertical direction or 6.7° around horizontal direction, the laser could still operate stably. For the Q-switched operation, the pulse energy of Ho:YAG laser was 9.9 mJ with a pulse width of 53 ns at the repetition rate of 100 Hz, resulting in a peak power of 186.8 kW. The beam quality factor M2 of Ho:YAG laser was 1.3.

Transmission of a microwave cavity coupled to localized Shiba states

We consider a strongly correlated quantum dot, tunnel coupled to two superconducting leads and capacitively coupled to a single mode microwave cavity. When the superconducting gap is the largest energy scale, multiple Shiba states are formed inside the gap. The competition of these states for the ground state signals a quantum phase transition. We demonstrate that photonic measurements can be used to probe such localized Shiba states. Moreover, the quantum phase transition can be pinpointed exactly from the sudden change in the transmission signal. Calculations were performed using the numerical renormalization group approach.

Systematic analysis of optical gradient force in photonic crystal nanobeam cavities.

In this work, we provide systematic analysis of the optical force for a particle trapped in the waveguide/cavity/waveguide system. The theoretical analysis shows that the optical trapping force is proportional to QT1/2/V for the particle at a fixed position. We provide numerical proof for the proposed principles and systematically optimize the design recipe to investigate optical tapping force of photonic crystal (PhC) nanobeam cavities. The numerical results are in accordance with theoretical analysis and show that the maximum optical trapping force for a particle occurs at the transmission of cavity around 0.25 and the maxima are almost the same for different PhC cavities.

Optomechanically induced transparency associated with steady-state entanglement

We theoretically investigate a two-cavity optomechanical system in which a cavity (cavity $a$) couples to a mechanical resonator via radiation pressure and to another cavity (cavity $c$) via a common waveguide. In the excitation of a strong pump filed to cavity $a$, the steady-state entanglement between cavity $a$ and $c$, as a quantum channel, can be generated, which provides an indirect optical pathway to excite cavity $c$ by means of the pump filed. Quantum interference between the direct and indirect optical pathways gives rise to an optomechanically induced transparency appearing in the probe transmission of cavity $c$. Unlike in a typical optomechanically induced transparency effect, the electromagnetical control of the transmission is implemented by resorting to the quantum channel. Furthermore, the coupling strength of the two cavities is an important factor of the quantum channel, which can influence the width of the transparency window and the bistable behavior of the mean photon number in cavity $a$. We also illustrate that the electromagnetical control via quantum channel can be exploited to implement the optical switch and the slow light.

Elastic wave scattering by periodic axisymmetric cavities in viscoelastic materials : theory and experiment

The reflection, transmission and absorption performance of periodic axisymmetric cavity in viscoelastic materials are analyzed by multiple scattering(MS) method. Based on MS method of elastic wave, the transition matrix between the incident wave and scattered wave is obtained by the numerical integrals for cavity surface. Meanwhile, the complex modulus of viscoelastic materials is measured by dynamic mechanical thermal analysis and time-temerature equivalent theory. With transfer function method in water tube, the absorption coefficient curves of different specimens of rubber materials containing cylindrical cavities are obtained. The measuring results are compared with that of MS method and also verified experimentally. The results indicate energy attenuation in viscoelastic materials depends on cavity scattering properties.

Optomechanical dynamics in detuned whispering-gallery modes cavity

The dynamics of a microresonator in detuned whispering-gallery modes (WGM) cavity opto-mechanical system are investigated by the quantum Langevin equation. A WGM cavity coupling to two parallel waveguides is devised to study the transmission and reflection of this system. In single mode WGM cavity, without optomechanical coupling, both the transmission and reflection of the cavity present a Lorentzian dip and peak. When the coupling between the cavity mode and mechanical mode is considered, the transmission and reflection of the optomechanical cavity show “W” and “M” shape mode splitting. Moreover, under the action of a controlling and a probe laser, the output field at the probe frequency presents electromagnetically induced transparency (EIT)-like spectrum in the system. We give the physical origin of EIT-like and the pump-probe response for the WGM shares all the features of the Λ system in atoms. Further, due to backscattering, the two traveling waves in WGM are coupled with a rate γ. The transmission and reflection of the optomechanical cavity display three modes splitting in the spectra with optomechanical coupling between the two cavity modes and the mechanical mode.

Measurement of the internal state of a single atom without energy exchange

A measurement necessarily changes the quantum state being measured, a phenomenon known as back-action. Real measurements, however, almost always cause a much stronger back-action than is required by the laws of quantum mechanics. Quantum non-demolition measurements have been devised that keep the additional back-action entirely within observables other than the one being measured. However, this back-action on other observables often imposes its own constraints. In particular, free-space optical detection methods for single atoms and ions (such as the shelving technique, a sensitive and well-developed method) inevitably require spontaneous scattering, even in the dispersive regime. This causes irreversible energy exchange (heating), which is a limitation in atom-based quantum information processing, where it obviates straightforward reuse of the qubit. No such energy exchange is required by quantum mechanics. Here we experimentally demonstrate optical detection of an atomic qubit with significantly less than one spontaneous scattering event. We measure the transmission and reflection of an optical cavity containing the atom. In addition to the qubit detection itself, we quantitatively measure how much spontaneous scattering has occurred. This allows us to relate the information gained to the amount of spontaneous emission, and we obtain a detection error below 10 per cent while scattering less than 0.2 photons on average. Furthermore, we perform a quantum Zeno-type experiment to quantify the measurement back-action, and find that every incident photon leads to an almost complete state collapse. Together, these results constitute a full experimental characterization of a quantum measurement in the 'energy exchange-free' regime below a single spontaneous emission event. Besides its fundamental interest, this approach could significantly simplify proposed neutral-atom quantum computation schemes, and may enable sensitive detection of molecules and atoms lacking closed transitions.

Ultranarrow resonance peaks in the transmission and reflection spectra of a photonic crystal cavity with Raman gain

The Raman gain of a probe light in a three-state $\ensuremath{\Lambda}$ scheme placed into a defect of a one-dimensional photonic crystal is studied theoretically. We show that there exists a pump intensity range, where the transmission and reflection spectra of the probe field exhibit simultaneously occurring narrow peaks (resonances) whose position is determined by the Raman resonance. Transmission and reflection coefficients can be larger than unity at pump intensities on the order of tens of $\ensuremath{\mu}\text{W}/{\text{cm}}^{2}$. When the pump intensity is outside this region, the peak in the transmission spectrum turns into a narrow dip. The nature of narrow resonances is attributed to a drastic dispersion of the nonlinear refractive index in the vicinity of the Raman transition, which leads to a significant reduction in the group velocity of the probe wave.

Efficient noise suppression of an amplified diode-laser by optical filtering and resonant optical feedback

We present the noise suppression of an amplified diode laser by using an optical filter and resonant optical feedback. The intensity noise of the amplified diode laser has been significantly decreased by using the optical filter cavity. It was further suppressed and reached the shot noise limit at 15 MHz by introducing resonant optical feedback from the transmission of the filter cavity. The filter cavity transmits 53% of injection power, and the output power of the filter cavity is more than 200 mW. The observed frequency fluctuations were less than 100 kHz in one minute. This level of noise suppression and output power may allow diode lasers to be utilized in many quantum-optics experiments.

Probabilistic generation of entanglement in optical cavities.

We propose to produce entanglement by measuring the reflection from an optical cavity. Conditioned on the detection of a reflected photon, pairs of atoms in the cavity are prepared in maximally entangled states. The success probability depends on the cavity parameters, but high quality entangled states may be produced with a high probability even for cavities of moderate quality.

Measurement of birefringence of low-loss, high-reflectance coating of m-axis sapphire

The birefringence of a low-loss, high-reflectance coating applied to an 8-cm-diameter sapphire crystal grown in the m-axis direction has been mapped. By monitoring the transmission of a high-finesse Fabry-Perot cavity as a function of the polarization of the input light, we find an upper limit for the magnitude of the birefringence of 2.5 x 10(-4) rad and an upper limit in the variation in direction of the birefringence of 10 deg. These values are sufficiently small to allow consideration of m-axis sapphire as a substrate material for the optics of the advanced detector at the Laser Interferometer Gravitational Wave Observatory.

CO/sub 2/ laser stabilization to 0.1-Hz level using external electrooptic modulation

We have developed a frequency stabilization scheme for CO/sub 2/ lasers using only external modulation via an electrooptic modulator (EOM). One of the two laser sidebands which are generated by the EOM and frequency-modulated is set in resonance with a Fabry-Perot cavity, itself filled with OsO/sub 4/ as an absorber. The saturation signal of an OsO/sub 4/ line detected in transmission of the Fabry-Perot cavity is used for stabilization. We obtained a stability of 0.1 Hz (/spl Delta//spl nu///spl nu/=3.5 10/sup -15/) on a 100-s time scale, and a reproducibility up to 10 Hz with the strongest OsO/sub 4/ reference lines. These results largely improve the performance of our previous setup for which modulation was applied through piezoelectric transducers. Further, the stabilized laser is not frequency-modulated and is easily tunable.

Spectral purity and long-term stability of CO/sub 2/ lasers at the Hertz level

Ultra-high-resolution spectroscopy and metrology require very stable lasers with a high-spectral purity. For spectroscopy with a resolution in the range 10-100 Hz at 30 THz, we are developing a new stabilization scheme which acts separately on the long and short term stabilities. We present the results achieved with the first part of our new scheme, which is based upon the stabilization on a saturation signal detected in transmission of an active Fabry-Perot cavity. With a laser linewidth of 3.4 Hz (FWHM) and a flicker plateau of 0.7 Hz (/spl Delta//spl nu///spl nu/=2.10/sup -14/) obtained using a strong OsO/sub 4/ line as reference, this stabilization system already improves the both short and long-term stabilities obtained by our previous setup which involved an external cell instead of a Fabry-Perot cavity. We present also the results using a CO/sub 2/ laser line as frequency reference. >

Efficient self-mode locking of continuous-wave solid-state lasers with resonant nonlinearity in an additional cavity

Parameters of the efficient mode-locking of cw solid-state lasers with saturable absorber in the additional cavity are found on the basis of the laser generation fluctuation model. These parameters form closed ranges. The main features of the efficient mode- locking are associated with the transmission of the additional cavity as a function of the field intensity. It is shown that due to the resonant nonlinearity the efficient mode-locking takes place in the absence of the interferometrical matching of the lengths of the master and additional cavities. It also takes place in the case of the difference of their lengths of up to the value for which the delay of the pulse from the additional cavity according to generation pulse becomes comparable with generation pulse duration.

Effective self-mode-locking of cw solid-state lasers with a resonant nonlinearity in an additional cavity

A fluctuation model of the operation of a cw solid-state laser with an additional cavity containing a saturable absorber is used to identify the effective self-mode-locking ranges which are closed areas when plotted in terms of the laser parameters. The main features of effective mode locking are related to the behaviour of the transmission of the additional cavity, considered as a function of the field intensity. It is shown that a resonant nonlinearity ensures effective mode locking both in the absence of interferometric matching of the cavity lengths and in the presence of a 'macromismatch' of their lengths when the delay of the field from the additional cavity relative to the lasing pulse is comparable with the pulse duration.

Influence of self-absorption on output power characteristics of a high-pressure cw CO2 laser

Absorption of intracavity radiation by CO2 molecules in an unexcited region has detrimental effects on output power characteristics, especially above a certain level of output power, i.e., the threshold level. These absorption effects have been investigated experimentally in detail. The threshold level depends both on CO2 concentration of the laser gas and on the mirror transmission of the optical cavity. It is found from these dependences that the absorption effect becomes serious above ∼0.2 W/cm3, which is the density of optical power absorbed by the unexcited CO2 molecules. The influence of self-absorption on the laser efficiency and the oscillating line of 10.4-μm band can be explained well by a usual theory for laser oscillation. Furthermore, a novel method for monitoring the concentration of CO2 molecules is demonstrated.

PHOTOCHROMIC CHANGE IN REFRACTIVE INDEX

Light-induced changes in the refractive index of transition metal doped SrTiO3 has been observed. This is the first observation of photochromic index of refraction changes. The measurements are made by observing the variation of transmission of a Fabry-Perot cavity made of the material studied. Changes in the index of refraction of 1–5 × 10−5 per unit change in optical density per centimeter are found. These values agree reasonably well with values calculated from the measured absorption curves.