Laser stabilization

The stabilization of a relatively simple optoelectronic oscillator tunable across the X-band based on a laser subjected to optical feedback is achieved. Specifically, a resonance effect based on locking the two inherent frequencies of the system, as well as, self-modulation were utilized to achieve a sub-ps phase jitter.

We have measured the electronic absorption spectrum of the oxygen (02) A band b 11+(v' = 0)-X 3 J-(V"1 = 0), near 760 nm in room air by using a newly available external-cavity diode laser. The external-cavity diode laser permitted a continuous, single-mode scan of the P branch of ambient oxygen by 2f modulation spectroscopy. The external-cavity diode laser opens up many applications limited in the past by the noncontinuous tunability of standard monolithic Fabry-Perot cavity laser designs. Specifically, absorption transitions that coincide with the gain bandwidth of any available diode laser (635 to 1550 nm) may now be reached without the problems and limitations imposed by mode hops inherent in standard Fabry-Perot cavity designs.

The frequency comb of an optical resonator is a naturally large set of exquisitely well defined quantum systems, such as in the broadband mode-locked lasers which have redefined time/frequency metrology and ultraprecise measurements in recent years. High coherence can therefore be expected in the quantum version of the frequency comb, in which nonlinear interactions couple different cavity modes, as can be modeled by different forms of graph states. We show that is possible to thereby generate states of interest to quantum metrology and computing, such as multipartite entangled cluster and Greenberger-Horne-Zeilinger states.

The back-reflection of emitted laser beam (optical feedback, also know as selfmixing) from various external interfaces are sufficient to cause instability, and prohibiting its use in various fields such as communication, spectroscopy, imaging to name a few. So it is desirable to study the laser dynamics and the conditions causing it to be stable in spite of strong optical feedback. With the aid of mathematical formulation, simulation and backed by experimental evidences, it is demonstrated that the frequency deviation of the laser emission due to current (intensity) modulation alters the dynamic state and boundary conditions of the system such that even under large optical feedback strength, the laser may attain stability and retain single modal state. The frequency deviation resulting from former is shown to modify the phase of the system in opposite direction to that induced by the later, showing that there exists an optimal modulation current which compensates the effect of optical feedback and may be used to retain the laser in single modal stationary state. The method thus provides a methodology to avoid optical feedback-induced instability in semiconductor lasers by using the proper amplitude of current (intensity) modulation.

We report a simple technique for stabilization of a laser frequency at the wings of an atomic resonance. The reference signal used for stabilization issues from interference effects obtained in a low-quality cavity filled with a resonant atomic vapour. For a frequency detuned at 2.6 GHz from the 133 Cs D 2 6S 1/2 F=4 to 6P 3/2 F'= 5 transition, the fractional frequency Allan deviation is 10 -8 for averaging times of 300 s, corresponding to a frequency deviation of 4 MHz. Adequate choice of the atomic density and of the cell thickness allows locking the laser at detunings larger than 10 GHz. Such a simple technique does not require magnetic fields or signal modulation.

Data students collect from the typical advanced undergraduate laboratory on Saturated Absorption Spectroscopy (SAS) of rubidium can be used to measure the isotope shift and thus leads to an estimate of the isotopic ground state energy shift. This helps students refine their `picture' of the atomic ground state. We describe theoretically why this laboratory works well with free-running laser diodes, demonstrate it experimentally using these lasers tuned to either principal near-infrared transitions, and show an extension of the laboratory using the modulation transfer spectroscopy method.

Wavelength tuning and spectral characteristics of commercially available standard laser diodes are far from ideal, and thus many applications in the near infrared are limited to the use of relatively expensive distributed feedback (DFB) laser diodes. External cavity diode lasers (ECDL), ...

this an external controller is constructed to study the effect of temperature on the electrical output of diode laser. and from our observations of the diode laser's output The system is very effective, stabilizing the temperature within an accuracy of ±0.1 • C, provide the highest heat dissipation capability. This controller tended of to stability at the higher temperatures.The temperature controller did show a good ability to maintain the temperature at the setting point. As a result, this temperature control system can supply a stabilized laser diode system to make it remain at almost the same wavelength. In addition, the tendency of this laser diode system to stability with higher temperatures.

A simple result of scalar diffraction theory is used to derive the round trip phase accrual of a plane wave in dye laser oscillators containing gratings. This is used to determine configurations where the standing wave condition is satisfied at the feedback wavelength throughout an angle scan. We find that at least one such exactly synchronous configuration always exists regardless of oscillator type.

We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-section quantum dash lasers emitting at ~1.55 µm and operating at ~21 GHz repetition rate, subjected to single and dual loop optical feedback into the gain section, over a wide range of feedback delay. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual-loop configurations. We demonstrate that dual-loop feedback with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, 10 – 50× better than single-loop feedback. In addition, for dual-loop configurations, under fully resonant conditions, phase noise is reduced to 295 fs [10 kHz – 100 MHz], the RF linewidth narrows to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual-loop optical feedback with separate fine tuning of both external cavities is far superior to single-loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

We report a simple technique for stabilization of a laser frequency at the wings of an atomic resonance. The reference signal used for stabilization issues from interference effects obtained in a low-quality cavity filled with a resonant atomic vapour. For a frequency detuned 2.6 GHz from the 133 Cs D 2 6S 1 2 F = 4 to 6P 3 2 F' = 5 transition, the fractional frequency Allan deviation is 10 −8 for averaging times of 300 s, corresponding to a frequency deviation of 4 MHz. Adequate choice of the atomic density and of the cell thickness allows locking the laser at detunings larger than 10 GHz. Such a simple technique does not require magnetic fields or signal modulation.

Feedback phenomenon in laser diodes is applied to low-frequency vibration measurement in the micrometer range on poorly reflecting targets. The laser diode is frequency modulated. Its beam is focused on the vibrating target, and backscattered light is fed back into the laser. The optical laser diode power variation is processed to measure the frequency and amplitude of low-frequency vibrations of amplitude, ϳ100 nm to 10 m. Experimental results for sinusoidal and triangular vibrations are compared with theory.

Mode stability is an important performance characteristic of external cavity diode lasers (ECDLs). It has been well established that the continuous mode-hop-free tuning range of a grating-feedback ECDL can be optimized by rotating the grating about a specific pivot location. We show that similar results can be obtained for other more convenient pivot locations by choosing instead the cavity length and grating location. The relative importance of the temperature stability of the diode and of the external cavity is also evaluated. We show that mechanically simple ECDL designs, using mostly standard components, can readily achieve a 35 GHz mode-hop-free tuning range at 780 nm.

We present an experimental observation of phase locking effects in the intensity noise spectrum of a semiconductor laser. These noise correlations are created in the medium by coherent carrier-population oscillations induced by the beatnote between the lasing and non-lasing modes of the laser. This phase locking leads to a modification of the intensity noise profile at around the cavity free-spectral-range value. The noise correlations are evidenced by varying the relative phase shift between the laser mode and the non-lasing adjacent side modes.