Jingbiao Chen

Note: Demonstration of an external-cavity diode laser system immune to current and temperature fluctuations

We demonstrate an external-cavity laser system using an anti-reflection coated laser diode as gain medium with about 60 nm fluorescence spectrum, and a Rb Faraday anomalous dispersion optical filter (FADOF) as frequency-selecting element with a transmission bandwidth of 1.3 GHz. With 6.4% optical feedback, a single stable longitudinal mode is obtained with a linewidth of 69 kHz. The wavelength of this laser is operating within the center of the highest transmission peak of FADOF over a diode current range from 55 mA to 142 mA and a diode temperature range from 15 °C to 35 °C, thus it is immune to the fluctuations of current and temperature.

Optical lattice laser

Atoms with narrow-linewidth transition trapped within the Lamb-Dick regime of optical lattice are proposed be used as laser gain medium to build a laser. The gain medium atoms can be the alkaline-earth species, Magnesium, Calcium, and Strontium, including Ytterbium. These atoms possess promising super-narrow optical clock transitions, but here, this clock transition is proposed to be used as the lasing transition of the output laser. This optical lattice laser with expected super-narrow linewidth is an active optical clock with high accuracy and stability.

Demonstration of an excited-state Faraday anomalous dispersion optical filter at 1529 nm by use of an electrodeless discharge rubidium vapor lamp

An excited-state Faraday anomalous dispersion optical filter (ESFADOF) operating on the rubidium 5P3/2-4D5/2 transition (1529.4 nm in vacuum) is demonstrated, which utilizes an electrodeless discharge lamp rather than a laser-pumped Rb vapor cell as in a traditional ESFADOF system. When the lamp operates in the red mode with 3.5 W radio-frequency driving power, a twin-peak line-shaped transmission spectrum is obtained, which has a maximum transmittance of 21.9% (without taking into account the system loss and fluorescence background). ESFADOF by exploiting the 5P3/2-4D3/2 transition (1529.3 nm in vacuum) is also explored. A single-peak transmission spectrum with a maximum transmittance of about 3% is achieved. The electrodeless discharge lamp based ESFADOF holds promise for realizing a compact, low-cost, and good long-term frequency-stabilized laser system for optical communication applications.

Active optical clock based on four-level quantum system

Active optical clock, a new conception of atomic clock, has been proposed recently. In this work, we propose a scheme of active optical clock based on four-level quantum system. The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam. To three-level quantum system, they are mainly limited by light shift of pumping laser field. These limitations can be avoided effectively by applying the scheme proposed here. Rubidium atom four-level quantum system, as a typical example, is discussed. The population inversion between 6S1/2 and 5P3/2 states can be built up at a time scale of 10−6 s. With the mechanism of active optical clock, in which the cavity mode linewidth is much wider than that of the laser gain profile, it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory. An experimental configuration is designed to realize this active optical clock.

Electrodeless-discharge-vapor-lamp-based Faraday anomalous-dispersion optical filter

We report an excited-state Faraday anomalous-dispersion optical filter operating on the rubidium 5P(3/2)-5D(5/2) transition (775.9 nm in vacuum) without the use of a pump laser. An electrodeless discharge vapor lamp is employed to replace the Rb vapor cell in a traditional Faraday anomalous-dispersion optical filter system. Atoms can be excited by power rather than a complex frequency-locked pump laser. A proof-of-concept experimental demonstration with a maximum transmission of 1.9% and a filter bandwidth of 650 MHz is presented.

Novel MDM-PON scheme utilizing self-homodyne detection for high-speed/capacity access networks

In this paper, we propose a cost-effective, energy-saving mode-division-multiplexing passive optical network (MDM-PON) scheme utilizing self-homodyne detection for high-speed/capacity access network based on low modal-crosstalk few-mode fiber (FMF) and all-fiber mode multiplexer/demultiplexer (MUX/DEMUX). In the proposed scheme, one of the spatial modes is used to transmit a portion of signal carrier (namely pilot-tone) as the local oscillator (LO), while the others are used for signal-bearing channels. At the receiver, the pilot-tone and the signal can be separated without strong crosstalk and sent to the receiver for coherent detection. The spectral efficiency (SE) is significantly enhanced when multiple spatial channels are used. Meanwhile, the self-homodyne detection scheme can effectively suppress laser phase noise, which relaxes the requirement for the lasers line-width at the optical line terminal or optical network units (OLT/ONUs). The digital signal processing (DSP) at the receiver is also simplified since it removes the need for frequency offset compensation and complex phase correction, which reduces the computational complexity and energy consumption. Polarization division multiplexing (PDM) that offers doubled SE is also supported by the scheme. The proposed scheme is scalable to multi-wavelength application when wavelength MUX/DEMUX is utilized. Utilizing the proposed scheme, we demonstrate a proof of concept 4 × 40-Gb/s orthogonal frequency division multiplexing (OFDM) transmission over 55-km FMF using low modal-crosstalk two-mode FMF and MUX/DEMUX with error free operation. Compared with back to back case, less than 1-dB Q-factor penalty is observed after 55-km FMF of the four channels. Signal power and pilot-tone power are also optimized to achieve the optimal transmission performance.

Magic wavelengths for terahertz clock transitions

Magic wavelengths for laser trapping of boson isotopes of alkaline-earth metal atoms Sr, Ca, and Mg are investigated while considering terahertz clock transitions between the {sup 3}P{sub 0}, {sup 3}P{sub 1}, and {sup 3}P{sub 2} metastable triplet states. Our calculation shows that magic wavelengths for laser trapping do exist. This result is important because those metastable states have already been used to make accurate clocks in the terahertz frequency domain. Detailed discussions for magic wavelengths for terahertz clock transitions are given in this article.

Optical Clocks Based on Quantum Emitters

In this report, we discuss the new feature of optical clocks based on quantum emitters, including clock operating above threshold, which is a laser essentially used as an active optical clock, and clock operating under threshold. Comparing with the active microwave clock, hydrogen maser, excellent performance of optical clock based on quantum emitter is expected. Comparison between configurations of atomic beam and lattice trapped atoms is analyzed. Moreover, we also present the discussion on the possibility of Ramsey laser, a laser operating at the configuration of Ramsey separated oscillating fields

Faraday anomalous dispersion optical filter with a single transmission peak using a buffer-gas-filled rubidium cell

A Faraday anomalous dispersion optical filter (FADOF) with a single transmission peak is achieved by using a buffer-gas (argon, 2 Torr)-filled rubidium cell. At room temperature, the transmission is 0.2% and the bandwidth of the transmission peak is 0.65 GHz. At a temperature of 63° C, the transmission rises to a maximum of 30.6%, with a bandwidth of 1.41 GHz. This FADOF may replace the use of interference filters or virtually imaged phased arrays in imaging modalities.

Diode laser operating on an atomic transition limited by an isotope ⁸⁷Rb Faraday filter at 780 nm.

We demonstrate an extended cavity Faraday laser system using an antireflection-coated laser diode as the gain medium and the isotope (87)Rb Faraday anomalous dispersion optical filter (FADOF) as the frequency selective device. Using this method, the laser wavelength works stably at the highest transmission peak of the isotope (87)Rb FADOF over the laser diode current from 55 to 140 mA and the temperature from 15°C to 35°C. Neither the current nor the temperature of the laser diode has significant influence on the output frequency. Compared with previous extended cavity laser systems operating at frequencies irrelevant to spectacular atomic transition lines, the laser system realized here provides a stable laser source with the frequency operating on atomic transitions for many practical applications.