Dijun Chen

Electromagnetically induced grating in asymmetric quantum wells via Fano interference

We propose a scheme for obtaining an electromagnetically induced grating in an asymmetric semiconductor quantum well (QW) structure via Fano interference. In our structure, owing to Fano interference, the diffraction intensity of the grating, especially the first-order diffraction, can be significantly enhanced. The diffraction efficiency of the grating can be controlled efficiently by tuning the control field intensity, the interaction length, the coupling strength of tunneling, etc. This investigation may be used to develop novel photonic devices in semiconductor QW systems.

Laser phase and frequency noise measurement by Michelson interferometer composed of a 3 × 3 optical fiber coupler.

A laser phase and frequency noise measurement method by an unbalanced Michelson interferometer composed of a 3 × 3 optical fiber coupler is proposed. The relations and differences of the power spectral density (PSD) of differential phase and frequency fluctuation, PSD of instantaneous phase and frequency fluctuation, phase noise and linewidth are derived strictly and discussed carefully. The method obtains the noise features of a narrow linewidth laser conveniently without any specific assumptions or noise models. The technique is also used to characterize the noise features of a narrow linewidth external-cavity semiconductor laser, which confirms the correction and robustness of the method.

Precision and broadband frequency swept laser source based on high-order modulation-sideband injection-locking

A precision and broadband laser frequency swept technique is experimentally demonstrated. Using synchronous current compensation, a slave diode laser is dynamically injection-locked to a specific high-order modulation-sideband of a narrow-linewidth master laser modulated by an electro-optic modulator (EOM), whose driven radio frequency (RF) signal can be agilely, precisely controlled by a frequency synthesizer, and the high-order modulation-sideband enables multiplied sweep range and tuning rate. By using 5th order sideband injection-locking, the original tuning range of 3 GHz and tuning rate of 0.5 THz/s is multiplied by 5 times to 15 GHz and 2.5 THz/s respectively. The slave laser has a 3 dB-linewidth of 2.5 kHz which is the same to the master laser. The settling time response of a 10 MHz frequency switching is 2.5 µs. By using higher-order modulation-sideband and optimized experiment parameters, an extended sweep range and rate could be expected.

Tunable External Cavity Diode Laser With a PLZT Electrooptic Ceramic Deflector

A stable tunable diode laser which uses an electrooptic deflector incorporated into a Littrow-type external cavity as a wavelength tunable element is proposed and demonstrated. The deflector is fabricated by lead lanthanum zirconate titanate (PLZT) electrooptic ceramic with high quadratic electrooptic effect. Two half-wave plates and a large angle triangular electrode of PLZT electrooptic ceramic are designed to acquire a high frequency-voltage tuning ratio. By adjusting the voltage applied to the deflector, a large single-mode tuning range of 420 GHz (including mode hops) and a frequency-voltage tuning ratio of 840 GHz/kV have been achieved at 780.5 nm.

Observation of multi-electromagnetically induced transparency in V-type rubidium atoms

A detailed experimental investigation and theoretical analysis have been made in the V-type Rb atomic medium. Seven induced transparency windows, including a central double-peak-structure, have been observed experimentally when a coupling field and a probe field are applied into the ground and first excited states. By taking into account the hyperfine splitting of the excited state, our theoretical analysis gives good explanation for the observed phenomena.

Fast optical frequency sweeping using voltage controlled oscillator driven single sideband modulation combined with injection locking.

An ultrafast optical frequency sweeping technique for narrow linewidth lasers is reported. This technique exploits the large frequency modulation bandwidth of a wideband voltage controlled oscillator (VCO) and a high speed electro-optic dual parallel Mach-Zehnder modulator (DPMZM) which works on the state of carrier suppressed single sideband modulation(CS-SSB). Optical frequency sweeping of a narrow linewidth fiber laser with 3.85 GHz sweeping range and 80 GHz/μs tuning speed is demonstrated, which is an extremely high tuning speed for frequency sweeping of narrow linewidth lasers. In addition, injection locking technique is adopted to improve the sweepers low optical power output and small side-mode suppression ratio (SMSR).

Modulation-free frequency stabilization of external-cavity diode laser based on a phase-difference biased Sagnac interferometer

We propose a modulation-free technique for frequency stabilization of an external-cavity diode laser (ECDL) by using a phase-difference biased Sagnac interferometer to produce dispersion spectroscopic error signals. A half-wave plate and a total internal reflection prism are inserted into the loop to provide a phase-difference bias between the clockwise and counterclockwise beams with perpendicular polarizations, instead of the previous method with misaligned optical paths. In the experiments, the frequency of the Littman-Metcalf configuration ECDL is locked at the transition of the Rb atomic vapor, and the frequency fluctuation is suppressed from 8 to less than 0.5 MHz peak to peak. It is shown that this scheme is simple, robust, low cost, and it shows promise for use in a variety of related applications.

Instabilities in a grating feedback external cavity semiconductor laser

Output power fluctuations in a grating external cavity diode laser with Littman configuration are described, showing peculiar chaotic behaviors of self-pulsation at the L-I curve kink points. Different spectral characteristics with multiple peaks are observed at upper and lower state of the self-pulsation. It is found also that P-N junction voltage jumps in a same pace with the pulsation. The observed phenomena reflect competition between different longitudinal modes, and transient variation of transverse modes in addition. These experimental results may contain information about the mechanisms of the chaotic instability in strong filtered feedback semiconductor lasers.

Cavity linewidth narrowing by optical pumping-assisted electromagnetically induced transparency in V-type rubidium at room temperature

A tunable high resolution frequency reference is constructed using the narrowed cavity-linewidth by the optical pumping-assisted V-type electromagnetically induced transparency (EIT). At room temperature, the optical pumping effect will increase the transparency for the V-type EIT and therefore the cavity-linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity-linewidth narrowing is observed in all of them. More importantly, we find that the cavity-linewidth can keep at 1.2MHz in a wide frequency range of 100MHz by utilizing the central EIT. This property provides a novel way for constructing high resolution tunable frequency reference via the intracavity EIT.A detailed experimental investigation is made in the intracavity V-type electromagnetically induced transparency (EIT) of the Rb atomic medium at room temperature. The optical pumping effect will increase the transparency for the V-type EIT at room temperature and therefore the cavity linewidth can be narrowed apparently. For the seven EITs observed in our previous study, cavity linewidth narrowing is observed in all of them. More importantly, we find that the cavity linewidth can keep at 1.2 MHz over a wide frequency range of 100 MHz by utilizing the central double-peak-structure EIT. This property provides a novel way for constructing a high resolution tunable frequency reference via the intracavity EIT.

Polarization Characteristics of an External Cavity Diode Laser With Littman–Metcalf Configuration

Polarization characteristics of an external cavity diode laser (ECDL) in Littman configuration with a diffraction grating are presented in this letter. Using a conventional analyzer, it is found that both linear polarized and elliptical polarized (EP) emission can be obtained from the ECDL. It is also an EP state in the laser cavity when the output is in EP state. Experimental results indicate that the grating we used is a polarization-conversion element for both of the zeroth- and first-order diffractions. Brief explanations and basic equations are given in this letter.