sub-MHz Linewidth Research Articles

Blue GaN-based DFB laser diode with sub-MHz linewidth

Distributed feedback laser diodes (DFBs) serve as simple, compact, narrow-band light sources supporting a wide range of photonic applications. Typical linewidths are on the order of sub-MHz for free-running III-V DFBs at infrared wavelengths, but linewidths of short-wavelength GaN-based DFBs are considerably worse or unreported. Here, we present a free-running InGaN DFB operating at 443 nm with an intrinsic linewidth of 685 kHz at a continuous wave output power of 40 mW. This performance is achieved using a first-order embedded hydrogen silsesquioxane (HSQ) surface grating. The frequency noise is measured using a cross-correlated self-heterodyne frequency discriminator, and two estimations of integrated linewidth are evaluated using 1/π integration and β-separation line integration methods.

O-band single-photon quantum key distributor master-to-slave injection-locked DFBLD pair

In comparison with the rapidly developing progress on the optical C-band (1525-1565 nm) master-to-slave injection-locked transmitter to perform the coherent single-photon quantum key distribution (QKD), the development on the O-band (1250-1350 nm) QKD transmitter is somewhat delayed as the commercially available wavelength-matched narrow-linewidth distributed feedback laser diode (DFBLD) pair is hardly accessible up to now. By using the DFBLDs with only sub-MHz linewidth and relatively deviated wavelength for the first time, this work demonstrates the optically differential-phase-shift-keying (DPS) QKD by an O-band master-to-slave injection-locked DFBLD pair. The master and slave DFBLDs with wavelength fluctuations of ±0.05% and ±0.2 pm are controlled by a thermo-electric cooler with a feedback gain of 100. The 1-bit delay interferometer (DI) under thermo-insulation maintains its visibility at >96% with dPo/Po and dPo/dt measured below ±0.1% and ±1 × 10−3 mW/s. By RZ-OOK modulating the master DFBLD with step-like power coding at 150 µW to induce π phase shift in the injection-locked slave DFBLD, the rising-/falling-edge DPS envelope distortion of the slave DFBLD diminishes by decreasing the bias current of the master DFBLD from 7Ith (35 mA) to 2Ith (10 mA). This phenomenon enables the 128-bit DPS-QKD transmission with a quantum bit-error rate (QBER) of 3.57% and a secure key rate of 3.524 kbit/s in the 6-km SMF link. The O-band injection-locked single-photon DPS-QKD bit-stream with a mean photon number of 0.2 #/bit minimizes its decoding QBER to 3.88% and 4.84% for 512-bit and 1024-bit, respectively.

Single-photon source with sub-MHz linewidth for cesium-based quantum information processing

Single-photon source with sub-MHz linewidth for cesium-based quantum information processing

422 Million intrinsic quality factor planar integrated all-waveguide resonator with sub-MHz linewidth

High quality-factor (Q) optical resonators are a key component for ultra-narrow linewidth lasers, frequency stabilization, precision spectroscopy and quantum applications. Integration in a photonic waveguide platform is key to reducing cost, size, power and sensitivity to environmental disturbances. However, to date, the Q of all-waveguide resonators has been relegated to below 260 Million. Here, we report a Si3N4 resonator with 422 Million intrinsic and 3.4 Billion absorption-limited Qs. The resonator has 453 kHz intrinsic, 906 kHz loaded, and 57 kHz absorption-limited linewidths and the corresponding 0.060 dB m−1 loss is the lowest reported to date for waveguides with deposited oxide upper cladding. These results are achieved through a careful reduction of scattering and absorption losses that we simulate, quantify and correlate to measurements. This advancement in waveguide resonator technology paves the way to all-waveguide Billion Q cavities for applications including nonlinear optics, atomic clocks, quantum photonics and high-capacity fiber communications.

Pulsed-pump phosphorus-doped fiber Raman amplifier around 1260 nm for applications in quantum non-linear optics.

We describe a fiber Raman amplifier for nanosecond and sub-nanosecond pulses centered around 1260 nm. The amplification takes place inside a 4.5-m-long polarization-maintaining phosphorus-doped fiber, pumped at 1080 nm by 3-ns-long pulses with a repetition rate of 200 kHz and up to 1.75 kW peak power. The input seed pulses are of sub-mW peak-power and minimal duration of 0.25 ns, carved out of a continuous-wave laser with sub-MHz linewidth. We obtain linearly polarized output pulses with peak powers of up to 1.4 kW, corresponding to peak-power conversion efficiency of over 80%. An ultrahigh small signal gain of 90 dB is achieved, and the signal-to-noise ratio 3 dB below the saturation power is above 20 dB. No significant temporal and spectral broadening is observed for output pulses up to 400 W peak power, and broadening at higher powers can be reduced by phase modulation of the seed pulse. Thus, nearly-transform-limited pulses with peak power up to 1 kW are obtained. Finally, we demonstrate the generation of pulses with controllable frequency chirp, pulses with variable width, and double pulses. This amplifier is thus suitable for coherent control of narrow atomic resonances, especially for the fast and coherent excitation of rubidium atoms to Rydberg states. These abilities open the way towards several important applications in quantum non-linear optics.

Linewidth Narrowing of Mutually Injection Locked Semiconductor Lasers with Short and Long Delay

A simple and effective approach to semiconductor laser linewidth narrowing via mutual injection locking is proposed and demonstrated in both short and long delay regimes. A theoretical analysis is presented to investigate the linewidth behavior of semiconductor lasers under mutual injection locking. Experimental demonstrations in short and long delay regimes are implemented by integrated devices and a fiber link system, respectively. Locking condition and dependence of laser linewidth on coupling parameters in both regimes are studied, confirming mutual injection locking as a practical method for linewidth narrowing. For the short-delayed integrated lasers, a linewidth narrowing factor of 13 is demonstrated and sub-MHz linewidth is achieved, while for the long-delayed lasers coupled by fiber link, the intrinsic linewidth is reduced to sub-100 Hz.

Self-injection locked blue laser

We demonstrate a 446.5 nm GaN semiconductor laser with sub-MHz linewidth. The linewidth reduction is achieved by locking the laser to a magnesium fluoride whispering gallery mode resonator characterized with 109 quality factor. Self-injection locking ensures single longitudinal mode operation of the laser.

Spectroscopy and laser cooling on the $${}^{1}S_{0}$$ 1 S 0 – $$\,^{3}P_{1}$$ 3 P 1 line in Yb via an injection-locked diode laser at 1,111.6 nm

We generate 555.8nm light with sub-MHz linewidth through the use of laser injection-locking of a semiconductor diode at 1111.6nm, followed by frequency doubling in a resonant cavity. The integrity of the injection lock is investigated by studying an offset-beat signal between slave and master lasers, by performing spectroscopy on the $(6s)^{2}$ $^{1}S_{0}-\,(6s6p)$ $^{3}P_{1}$ transition in magneto-optically trapped ytterbium, and by demonstrating additional laser cooling of $^{171}$Yb with the 555.8nm light. For the $^{1}S_{0}-$ $^{3}P_{1}$ spectroscopy, we confirm the linear dependence between ground state linewidth and the intensity of an off-resonant laser, namely, that used to cool Yb atoms in a $^{1}S_{0}-$ $^{1}P_{1}$ magneto-optical trap. Our results demonstrate the suitability of injection locked 1100-1130nm laser diodes as a source for sub-MHz linewidth radiation in the yellow-green spectrum.

Experimental Generation of Narrow-Band Paired Photons: from Damped Rabi Oscillation to Group Delay

We report the experimental generation of narrow-band paired photons through electromagnetically induced transparency and spontaneous four-wave mixing in a two-dimensional magneto-optical trap (2D MOT). By controlling the optical depth of the 2D MOT from 0 to 40, the temporal length of the generated narrow-band paired photons can be varied from 50 to 900 ns. The ‘transition’ between damped Rabi oscillation and group delay is observed undisputedly. In the damped Rabi oscillation regime, a violation factor of the Cauchy—Schwartz inequality as large as 6642 is observed. In the group delay regime, sub-MHz linewidth (∼ 0.65 MHz) paired photons are obtained with a generation rate of about 0.8 × 105 s−1.

Error-rate Floors in Differential n-level Phase-shift-keying Coherent Receivers employing Electronic Dispersion Equalisation

Abstract A model for the phase noise influence in differential n-level phase shift keying (nPSK) systems and 2n-level quadrature amplitude modulated (2nQAM) systems employing electronic dispersion equalization and quadruple carrier phase extraction is presented. The model includes the dispersion equalization enhanced local oscillator phase noise influence. Numerical results for phase noise error-rate floors are given for dual polarization (DQPSK, D16PSK and D64PSK) system configurations with basic baud-rate of 25 GS/s. The transmission distance in excess of 1000 km requires local oscillator lasers with sub-MHz linewidth.

I.C.E.: a transportable atomic inertial sensor for test in microgravity

We present the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (Interférométrie Cohérente pour l’Espace) collaboration. On-board laser systems have been developed based on fibre-optic components, which are insensitive to mechanical vibrations and acoustic noise, have sub-MHz line width, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum system has been built, and used for laser cooling and magneto-optical trapping. We will use a mixture of quantum degenerate gases, bosonic 87Rb and fermionic 40K, in order to find the optimal conditions for precision and sensitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20 s in an Airbus. We investigate the experimental limits of our apparatus, and show that the factors limiting the sensitivity of a long-interrogation-time atomic inertial sensor are the phase noise in reference-frequency generation for Raman-pulse atomic beam splitters and acceleration fluctuations during free fall.

High-Resolution Photoassociation Spectroscopy of Ultracold Ytterbium Atoms by Using the Intercombination Transition

We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested.

Novel Single Frequency and Broadly Tunable Laser Sources Developed at Coherent Technologies Inc. for Remote Sensing Applications

AbstractThis paper provides an overview of novel single frequency and broadly tunable laser technology being developed at Coherent Technologies, Inc. (CTI) for long-range remote sensing of hard targets and distributed targets from ground based and airborne platforms. In all these applications, the need for high beam quality and efficient high power operation is paramount. For many of the applications, it is also critical to control and measure frequency content of the emitted and collected light to a high degree of accuracy. For example, a sub-kHz linewidth is typically required for velocity and vibration imaging, and sub-MHz linewidth for some differential absorption lidar (DIAL) type measurements.

헤테로다인 방법을 이용한 펄스 증폭된 레이저빔의 주파수 Chirping연구

좁은 선폭을 갖는 연속 레이저 빔이 제이조화된 Nd:YAG레이저빔과 Bethune셀을 사용하여 좁은 선폭을 갖는 펄스 레이저빔이 생성되었다. 증폭된 펄스빔의 주파수 chirping정도는 헤테로다인 방법을 이용하여 측정되었으며, 헤테로다인 맥놀이신호로부터 순간적인 위상 변화량을 추출함으로서 분석되었다. 10 ns 펄스에 의해 MHz 이하의 선폭을 가지는 연속 레이저빔으로부터 증폭된 주파수 chirping은 80MHz정도로 매우 좁은 선폭의 증폭된 펄스 레이저빔이 얻어졌다. Amplified pulsed laser beam with narrow linewidth was generated from CW laser beam with narrow linewidth by using frequency doubled Nd:YAG laser beam and Bethune cell. The degree of the frequency chirping of the amplified pulse laser was measured by using the heterodyne method and obtained by calculating instantaneous phase change from heterodyne beating signals. The frequency chirping of amplified pulsed laser beam from CW laser beam with sub-MHz linewidth by 10 ns pulse was 80 MHz so that pulsed laser beam with very narrow linewidth was obtained.

Sub-MHz spectral linewidth in 1.5μm separate-confinementheterostructure (SCH) quantum-well DFB LDs

Extremely narrow spectral-linewidth characteristics in 1.5 mu m GaInAs/GaInAsP separate-confinement-heterostructure (SCH), quantum-well (QW), distributed-feedback, laser diodes (DFB LDs) are reported. Narrower linewidths were obtained in lasers with smaller numbers of quantum wells. Sub-MHz linewidth was achieved for the first time in single laser diodes. >