Compact Cavity Research Articles

Compact photonic crystal disk cavity optimized using the gentle confinement method and boundary design

A compact, novel photonic crystal cavity aimed at applications with strict area limitations is presented. Optimization shows that the gentle confinement method previously used for line-defect cavities can be applied to more limited geometries. It also shows that it is paramount to consider the boundary region to minimize in-plane losses. The investigation show that a near optimum boundary thickness can be found by considering the boundary region as a Fabry–Pérot resonator. This optimization strategy is shown to be deterministic in terms of resonance wavelength. For an optimized air-clad, silicon cavity, finite-difference time-domain simulations give Q-values as high as 75,000 which is comparable to other photonic crystal cavities of similar size.

All-fiber 250 MHz fundamental repetition rate pulsed laser with tilted fiber grating polarizer

We demonstrated a high fundamental repetition-rate pulsed erbium-doped fiber laser with all-fiber-integrated configuration. A novel scheme using a 45°-tilted fiber grating as the in-fiber polarizing element was employed to shorten the total cavity length and, thus, increase the fundamental repetition rate of the laser. Dissipative soliton pulses mode-locked with a fundamental repetition rate of 251.3 MHz and pulse duration of 96.7 fs have been achieved from the compact and all-fiber ring cavity laser. Additionally, passively Q-switched pulses were observed from this high fundamental repetition-rate fiber laser, which is the first report on Q-switched fiber laser using a tilted fiber grating.

Frequency noise suppression of a single mode laser with an unbalanced fiber interferometer for subnanometer interferometry.

We present a method of noise suppression of laser diodes by an unbalanced Michelson fiber interferometer. The unstabilized laser source is represented by compact planar waveguide external cavity laser module, ORIONTM (Redfern Integrated Optics, Inc.), working at 1540.57 nm with a 1.5-kHz linewidth. We built up the unbalanced Michelson interferometer with a 2.09 km-long arm based on the standard telecommunication single-mode fiber (SMF-28) spool to suppress the frequency noise by the servo-loop control by 20 dB to 40 dB within the Fourier frequency range, remaining the tuning range of the laser frequency.

ULTRASHORT MICROWAVE PULSE GENERATION BY PASSIVE PULSE COMPRESSION IN A COMPACT REVERBERANT CAVITY

In this paper, we demonstrate a device that is capable of generating an ultrashort (sub-nanosecond) high power microwave pulse by means of passive pulse compression in a compact reverberant cavity. The long duration input pulse into the cavity is created using time-reversal techniques, which allows the waveform to contain the inverse profile of the cavity phase distortion. When fed back into the cavity, the wave focusing at the output port results in a compressed ultrashort pulse with enhanced peak amplitude. We experimentally demonstrate a pulse compressor consisting of a 0.0074 m 3 cavity capable of generating a 130 picosecond pulse from an input waveform of 300 nanosecond duration with the peak gain of up to 19 dB.

Compact High-Peak-Power End-Pumped AlGaInAs Eye-Safe Laser With a Heat-Spreader Diamond Coated as a Cavity Mirror

We report on a high-peak-power end-pumped AlGaInAs laser at 1.52 μm with a linear plane-parallel cavity. A high-reflective coated diamond is utilized not only as the heat spreader but also as the front mirror simultaneously to make the laser cavity to be extremely compact. The average output power and the corresponding peak power under this cavity configuration is found to be up to 2.58 and 516 W separately at a repetition rate of 100 kHz and a pump power of 12 W corresponding to a peak power of 2.4 kW. The experimental results assure the promising application of dielectric coated diamond as a multifunctional optics to fulfill a high performance and compact cavity design.

Design of an Economical Compact Coaxial Cavity Combline Filter for 3G TD Base Station

The cross coupled microwave filter is widely used in the communication sub system .The synthesis of the cross coupled filter is from prescribed transmission zeros and return loss till the attainment of the coupling matrix of each cavity. A compact narrowband combline high rejection filter with cross coupled is presented. A configureiton using identical resonator post with capacitance-loading is introduced. Tested results show that with order-8 filter center frequency at 2017.5MHz, return loss lower than-25dB can be achieved over a relative bandwidth of 1.29%. A sample filter has been fabricated and tested result confirmed the theory result.

Ultrahigh-Q TE/TM dual-polarized photonic crystal holey fishbone-like nanobeam cavities

We propose and theoretically investigate a one-dimensional photonic crystal holey fishbone-like silicon nanobeam cavity that simultaneously supports both fundamental transverse-electric (TE) and second-order transverse-magnetic (TM) modes, and modes. Three-dimensional finite-difference time-domain simulations show that with thin cavity thickness and compact cavity size, the cavity possesses ultrahigh Q (, ), along with small mode volume and high confinement factor, for both and modes. We believe our proposed cavity could be beneficial for nonlinear frequency conversion, optomechanics and other applications where dual-polarized TE/TM modes are needed.

Self-Q-switched waveguide laser based on femtosecond laser inscribed Nd:Cr:YVO(4) crystal.

We report on the self-Q-switched laser operation of a monolithic Nd:Cr:YVO(4) channel waveguide cavity. Femtosecond laser inscription was used to fabricate a buried channel waveguide in the substrate. The Nd:Cr:YVO(4) crystal works as both the gain medium and the saturable absorber, which enables the realization of a self-Q-switched waveguide laser pumped at 808 nm and emitting at 1064 nm. The compact waveguide cavity achieved maximum output powers up to 57 mW, corresponding to a single-pulse energy of 22.8 nJ, at 2.3 MHz repetition rate with a pulse duration of 85 ns.

Carbon nanostructure-based saturable absorber mirror for a diode-pumped 500-MHz femtosecond Yb:KLu(WO4)2 laser.

We report a diode-pumped Yb:KLu(WO(4))(2) (Yb:KLuW) laser passively mode-locked by employing a carbon nanostructure-based multi-functional saturable absorber mirror. Two types of carbon nanostructures, single-walled carbon nanotubes (SWCNTs) and graphene, were deposited on a single dielectric mirror and applied both for stable mode-locking of the Yb:KLuW laser near 1050 nm in a compact cavity configuration. The carbon nanostructure mode-locked laser delivers 157-fs pulses with output powers of up to 85 mW at a repetition rate of 500 MHz.

All-Silicon Technology for High-$Q$ Evanescent Mode Cavity Tunable Resonators and Filters

This paper presents a new fabrication technology and the associated design parameters for realizing compact and widely-tunable cavity filters with a high unloaded quality factor (Q <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ) maintained throughout the analog tuning range. This all-silicon technology has been successfully employed to demonstrate tunable resonators in mobile form factors in the C, X, Ku, and K bands with simultaneous high unloaded quality factors (≥500) and tuning ratios (≥1:2). It is shown that by employing high-precision micro-fabrication techniques and careful modeling, the measured RF and tuning performance of the fabricated device closely match the simulated results. The capability of monolithic (system-on-chip) integration, low-cost batch processing, and compatibility with CMOS processing is some of the key advantages of this 3-D tunable filter fabrication technology over conventional approaches. This technology also has the potential to be extended to produce tunable resonators and filters in the millimeter wave region.

Blackbody thermal radiator with vertically aligned carbon nanotube coating

The effective emissivity of a cavity-type blackbody thermal radiator is greatly enhanced by a target disk with a coating of vertically aligned carbon nanotubes (CNT). The effective emissivity of this cavity is close to 1 and is less dependent on wavelength. Observed and calculated increases in radiance temperature owing to the use of the CNT disk show good agreement with each other and the dependence of the radiance temperature on the cavity depth is reduced substantially, thus enabling a compact cavity that can be effectively employed in the calibration of industrial radiation thermometers operating in a wide wavelength range.

Laser performance of diode-pumped Nd, Y-codoped CaF 2–SrF 2 mixed crystal

A disordered Nd, Y-codoped CaF2–SrF2 mixed crystal was obtained by the temperature gradient technique (TGT). The absorption and fluorescence spectra of the crystal were measured at room temperature. Diode-pumped continuous-wave (CW) and Q-switched laser operations were demonstrated at 1056 nm with a 0.65 at.% Nd, 10 at.% Y-codoped crystal, for the first time to our knowledge. The CW output power of 724 mW was obtained in a compact linear cavity. Also the Q-switched pulse characteristics of Nd, Y:CaF2–SrF2 laser crystal were reported based on Cr4+:YAG saturable absorbers in a folded cavity. The shortest pulse width of 110 ns and the highest peak power of 383 W were obtained when the initial transmission of the Cr4+:YAG crystals was 90%. The dependence of the operational parameters on the pump power was also investigated experimentally.

Yb:KYW planar waveguide laser Q-switched by evanescent-field interaction with carbon nanotubes

We report Q-switched operation of a planar waveguide laser by evanescent-field interaction with single-walled carbon nanotubes deposited on top of the waveguide. The saturable-absorber-integrated gain medium, which operates based on evanescent-field interaction, enables the realization of a diode-pumped 2.5-cm-long Q-switched Yb:KYW waveguide laser emitting at 1030 nm. With such a compact cavity design, we achieve maximum output powers of up to 30 mW, corresponding to a single-pulse energy of 124 nJ, at 241 kHz repetition rate. The shortest pulse duration of 433 ns is generated at a repetition rate of 231 kHz.

Highly efficient and compact cavity oscillator for high-power, optically pumped gas terahertz laser

We demonstrate a highly efficient and compact terahertz cavity oscillator that is based on z-cut crystal quartz used as the dichroic beam splitter, for the first time to the best of our knowledge. With D(2)O gas as the active medium, pumped with a multitransverse mode TEACO(2) laser, experimental verification was also presented to demonstrate the advantages of this cavity oscillator. With the cavity length of 120 cm, 7.4 mJ pulse energy at pulse repetition frequency of 6 Hz, pulse width of 90 ns, and peak power of 82.2 kW were achieved at a wavelength of 385 μm. Photon conversion efficiency (PCE) of 44% was obtained at the maximum output level from this terahertz cavity oscillator. Furthermore, to our knowledge, this PCE is the highest efficiency ever reported in D(2)O gas, 385 μm terahertz cavity laser systems. The beam quality or M(2) factor was found to be about 1.77.

Passive Q-switched mode locking of a diode-pumped Tm:SSO laser near 2 μm

With a fiber-coupled 790 nm laser diode array as the pump source and a 4 at.% Tm:Sc2SiO5 (Tm:SSO) crystal, laser action near 2 μm wavelength was successfully obtained with a compact four-mirror fold cavity. Using broadband carbon nanotube as the saturable absorber, a passively Q-switched mode-locked (QML) Tm:SSO laser is realized for the first time. 100% modulation depth of mode locking has been achieved. The duration of the mode-locked pulse is estimated to be about sub-100 ps with 92.6 MHz repetition rate within a Q-switched pulse envelope. The spectrum of the QML laser is centered at 1967.4 nm with a broad spectral region of ∼23 nm. A maximum average output power of 195 mW and Q-switched pulse energy of 4.7 μJ is obtained. The dependence of the operational parameters on pump power was also investigated experimentally.

Lasing in plasmon-induced transparency nanocavity

We propose a plasmon-induced transparency (PIT) nanocavity for achieving nanoscopic coherent light source. The compact cavity is constructed by a pair of detuned nano-stubs incorporated with four-level gain medium. The PIT response enables the reduction of the coupling loss from cavity to waveguide while keeping the cavity size unchanged, different from the end-facet Fabry-Pérot cavity in which the radiation loss decreases at the cost of size increment. In order to study the lasing behavior of surface plasmon wave in the PIT cavity, the self-consistent finite element method is employed to model the interactions between gain and propagating surface plasmons. The dynamics of the whole lasing process is observed, and the linear output-input relation is obtained for the single mode plasmon lasing. It is demonstrated that smaller stub-pair detuning provides stronger feedback inside the cavity. Consequently, the lasing threshold of pumping rate decreases quadratically with the decreasing of detuning. However, the output-input extraction efficiency will improve when the detuning is not so small. One of the advantages for the proposal is that the lasing output power from the cavity can directly couple towards the metal-dielectric-metal waveguide platform, facilitating the field of integrated plasmonic circuits and molecular-scale coherent light source.

Real-time vapor detection of nitroaromatic explosives by catalytic thermal dissociation blue diode laser cavity ring-down spectroscopy

A compact blue diode laser catalytic thermal dissociation cavity ring-down spectrometer (cTD–CRDS) to detect vapors of nitroaromatic explosives is described. The instrument uses heated platinum(IV) oxide catalyst to convert nitroaromatic compounds to NO2, which is detected at 405nm. Using the relatively volatile nitrobenzene as a test compound, we show by Fourier Transform Infrared Spectroscopy (FTIR) in off-line experiments that nitroaromatics can be quantitatively converted to NO2. The cTD–CRDS detection limit was 0.3parts-per-billion by volume (ppbv) and sufficiently low to allow the detection of a room temperature sample of 2,4,6-trinitrotoluene (TNT) without sample preconcentration.

A femtosecond hybrid mode-locking fiber ring laser at 409 MHz

We report on a 312 fs all-fiber ring laser with a fundamental repetition rate of 409 MHz based on an Er3+/Yb3+ codoped phosphate glass fiber, which is only 5.0 cm in length. Such a high repetition rate femtosecond fiber laser is realized by combining an optical integrated module and a hybrid mode-locking method, where a semiconductor saturable absorber mirror ensures the self-starting mode-locking and a nonlinear polarization evolution technique provides a pulse shortening mechanism. With a transmission-type saturable absorber, the fundamental repetition rate of a hybrid mode-locking all-fiber ring laser is expected to be further scaled up with a much more compact cavity structure.

Comb-calibrated frequency-modulated continuous-wave ladar for absolute distance measurements

We demonstrate a comb-calibrated frequency-modulated continuous-wave laser detection and ranging (FMCW ladar) system for absolute distance measurements. The FMCW ladar uses a compact external cavity laser that is swept quasi-sinusoidally over 1 THz at a 1 kHz rate. The system simultaneously records the heterodyne FMCW ladar signal and the instantaneous laser frequency at sweep rates up to 3400 THz/s, as measured against a free-running frequency comb (femtosecond fiber laser). Demodulation of the ladar signal against the instantaneous laser frequency yields the range to the target with 1 ms update rates, bandwidth-limited 130 μm resolution and a ~100 nm accuracy that is directly linked to the counted repetition rate of the comb. The precision is <100 nm at the 1 ms update rate and reaches ~6 nm for a 100 ms average.

High-bandwidth squeezed light at 1550 nm from a compact monolithic PPKTP cavity

We report the generation of squeezed vacuum states of light at 1550 nm with a broadband quantum noise reduction of up to 4.8 dB ranging from 5 MHz to 1.2 GHz sideband frequency. We used a custom-designed 2.6 mm long biconvex periodically-poled potassium titanyl phosphate (PPKTP) crystal. It featured reflectively coated end surfaces, 2.26 GHz of linewidth and generated the squeezing via optical parametric amplification. Two homodyne detectors with different quantum efficiencies and bandwidths were used to characterize the non-classical noise suppression. We measured squeezing values of up to 4.8 dB from 5 to 100 MHz and up to 3 dB from 100 MHz to 1.2 GHz. The squeezed vacuum measurements were limited by detection loss. We propose an improved detection scheme to measure up to 10 dB squeezing over 1 GHz. Our results of GHz bandwidth squeezed light generation provide new prospects for high-speed quantum key distribution.