Antireflection-coated Laser Diode Research Articles

Continuous frequency tuning of an external cavity diode laser significantly beyond the free spectral range by sweeping the injection current.

In this study, the focus is on continuously tuning an external cavity diode laser equipped with an antireflection-coated laser diode over a 14.8 GHz range, 4.5 times larger than the free spectral range, using only injection current sweeps. In contrast, the absence of antireflection coating led to a tuning range of only one-fifth of the free spectral range, accompanied by hysteresis on mode hops. Theoretical analysis of this observed hysteresis suggests that broad tuning can be achieved when the longitudinal modes of the solitary laser diode are eliminated through the antireflection coating.

A scalable laser system at 461 nm for laser cooling and trapping of Sr atoms

The realization of compact high-power narrow-linewidth laser sources in the visible range has been a long-standing interest for the atomic physics community, especially in the field of laser cooling and trapping of alkaline-earth and alkaline-earth-like atoms. We report a simple master-slave injection-locked laser system capable of generating 500 mW at 460.86 nm with a linewidth of 1.6 MHz to realize magneto-optical trapping of strontium atoms on the 5s^{2} ^{1}mathrm {S}_{0}-5s5p ^{1}mathrm {P}_{1} transition. The master laser used is an external cavity diode laser built with an anti-reflection coated laser diode in a Littrow configuration and the slave laser is built with a recently launched single mode high power GaN laser diode. We characterized the frequency noise, injection stability, spectral purity and relative intensity noise of the laser system. The reported laser system is used routinely to produce 10^7 strontium atoms at a temperature of 10 mK in a magneto-optical trap. The laser system offers a prominent alternative to the existing frequency-doubled laser systems in terms of cost, design flexibility, electrical power consumption, ease of scaling, intensity stability, and frequency tunability. The proposed system is also an effective solution for space-based experiments where a laser system’s size, weight, and electrical power consumption are crucial design parameters.

Antireflection coated semiconductor laser amplifier for Bose-Einstein condensation experiments

We present a slave laser highly suitable for the preparation and detection of 87Rb Bose-Einstein condensates (BEC). A highly anti-reflection coated laser diode serves as an optical amplifier, which requires neither active temperature stabilization nor dedicated equipment monitoring the spectral purity of the amplified light. The laser power can be controlled with a precision of 10 μW in 70 mW with relative fluctuations down to 2 × 10−4. Due to its simplicity and reliability, this slave laser will be a useful tool for laboratory, mobile, or even space-based cold-atom experiments. By the way of demonstration this slave laser was used as the sole 780 nm light-source in the production of 3 × 104 BECs in a hybrid magnetic/dipole trap.

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.

Photoluminescence excitation measurements using pressure-tuned laser diodes.

Pressure-tuned laser diodes in external cavity were used as tunable sources for photoluminescence excitation (PLE) spectroscopy. The method was demonstrated in the 720 nm-1070 nm spectral range using a few commercial laser diodes. The samples for PLE measurements were quantum-well structures grown on GaAs and on InP. The method is superior to standard PLE measurements using titanium sapphire laser because it can be extended to any spectral range where anti-reflection coated laser diodes are available.

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.

Flexible laser diode trace gas sensor based on cavity ringdown spectroscopy with an optical fiber-coupled high-finesse external-cavity diode laser

A flexible and portable trace nitrogen dioxide sensor based on cavity ringdown spectroscopy using an optical fiber-coupled high-finesse cavity was successfully demonstrated. Tailoring the spatial mode matching condition of the core of an optical fiber and high-finesse external cavity allows for effective optical feedback into an antireflection-coated laser diode for stable resonant enhancement of the external cavity. The external cavity, which works as a ringdown cavity, could be remotely located from the light source and receiver section by only a single mode optical fiber. The sensitivity was found to be 1.0×10−7 cm−1 in a compact 1-cm3 ringdown cavity volume.

Tapered-amplified antireflection-coated laser diodes for potassium and rubidium atomic-physics experiments

We present a system of room-temperature extended-cavity grating-diode lasers for production of light in the range of 760–790nm. The extension of the tuning range towards the blue is permitted by the weak feedback in the cavity: the diodes are antireflection coated, and the grating has just 10% reflectance. The light is then amplified using semiconductor tapered amplifiers to give more than 400mW of power. The outputs are shown to be suitable for atomic-physics experiments with potassium (767nm), rubidium (780nm), or both, of particular relevance to doubly degenerate boson-fermion mixtures.

Mode-locking external-cavity laser-diode sensor for displacement measurements of technical surfaces

A novel laser sensor for position measurements of technical solid-state surfaces is proposed. An external Fabry-Perot laser cavity is assembled by use of an antireflection-coated laser diode together with the technical surface. Mode locking results from pumping the laser diode synchronously to the mode spacing of the cavity. The laser cavity length, i.e., the distance to the measurement object, is determined by evaluation of the modulation transfer function of the cavity by means of a phase-locked loop. The mode-locking external-cavity laser sensor incorporates a resonance effect that results in highly resolving position and displacement measurements. More than a factor-of-10 higher resolution than with conventional nonresonant sensing principles is achieved. Results of the displacement measurements of various technical surfaces are reported. Experimental and theoretical investigations are in good agreement.

External cavity laser sensor using synchronously-pumped laser diode for position measurements of rough surfaces

A novel optical sensor for absolute position measurements of rough surfaces is presented. The technical surface acts as reflector of an external cavity for an antireflection-coated laser diode. Evaluation of the resulting mode spacing determines the laser cavity length, i.e. the distance to the rough surface. Modelocking by synchronous pumping of the laser diode allows highly-resolved measurements with position resolution of 5 µm and temporal resolution of 200 µs.

Chaotic self-pulsation and cross-modulation in a wavelength-selective external-cavity laser diode

Chaotic self-pulsation in a single wavelength external-cavity laser diode is observed. It is shown that the self-pulsation is caused by interdependencies between the optical output power and the compound cavity losses through the refractive index of the laser diode material. Refractive index changes result in a detuning between the externally selected wavelength and the weak internal-mode structure of the anti-reflection coated laser diode. This detuning is directly related to the compound cavity losses. On the one hand, a change in optical output power results in a change of the refractive index via the carrier density. On the other hand, it results in a change of refractive index via temperature changes. Compared to the carrier induced refractive index change, the temperature induced refractive index change is opposite in sign, a factor of /spl sim/10/sup 2/ smaller and slower. The switch-on and switch-off time of the self-pulsation is governed by the carrier life time. The repetition rate of the self-pulsation is governed by the thermal time constant and is in the megahertz region. Cross-modulation resulting from the thermal induced refractive index change is demonstrated. In a two-wavelength double external-cavity laser diode, optical power at one wavelength effects the optical power at the other wavelength. This cross-modulation is shown to be related to previous experiments on a laser neural network. A novel technique is introduced to measure the thermal impedance of a laser diode that is based on the cross-modulation.

All-optical flip-flop based on coupled laser diodes

An all optical set-reset flip flop is presented that is based on two coupled identical laser diodes. The lasers are coupled so that when one of the lasers lases it quenches lasing in the other laser. The state of the flip flop is determined by which laser is currently lasing. Rate equations are used to model the flip flop and obtain steady state characteristics. The flip flop is experimentally demonstrated by use of antireflection coated laser diodes and free space optics.

All-optical flip-flop based on coupled laser diodes

An all-optical set-reset flip-flop is presented that is based on two coupled identical laser diodes. The lasers are coupled so that when one of the lasers lases, it quenches lasing in the other laser. The state of the flip-flop is determined by which laser is currently lasing. Rate equations are used to model the flip-flop, and it is experimentally demonstrated by the use of antireflection-coated laser diodes and free-space optics. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 157-159, 2000.

Subkilohertz enhanced-power diode-laser spectrometer in the visible

We report on a high-performance diode-laser spectrometer operating near 657 nm with narrow linewidth (<0.6 kHz) , enhanced power (as much as 40 mW), and low drift (<10 Hz/s) . The spectrometer comprised an extended-cavity diode-laser frequency stabilized to a high-finesse optical resonator and a broad-area antireflection coated laser diode as an amplifier with a single-lobe emission pattern of good spatial purity. The spectrometer was used to record time-domain optical Ramsey spectra of laser-cooled Ca atoms with a resolution of 0.6 kHz.

Strongly anticorrelated twin beams from symmetric low-Q cavity semiconductor lasers under constant-current operation

We have observed a strong anticorrelation between the photocurrent fluctuations of two laser outputs from symmetric low-Q cavity laser diodes (LDs) driven far above the threshold in a constant-current mode. The degree of correlation is highly dependent on the mirror reflectivities of the cavity:nn-66% for the conventional LD with cleaved facets, and -90% for the antireflection-coated LD with residual mirror reflectivities of 5%. In the case of a cleaved LD, the sum of the photocurrent fluctuations of both laser outputs exhibits 2.8 dB noise reduction below the shot-noise level. This is the first observation of subshot-noise photocurrent fluctuations symmetric cavity LDs.

Applications of an extremely short strong-feedback configuration of an external-cavity laser diode system fabricated with GaAs-based integration technology

A composite-cavity laser diode is used to monitor the reflectivity or the displacement of the external-cavity mirror for micromechanical photonics devices. Optical disk bits are read out in the near field from the difference in medium reflectivity with an antireflection-coated laser diode and a photodiode. Microbeam vibration is also detected in the near field from the phase difference with an uncoated laser diode and a photodiode. In both cases the carrier-to-noise ratio is very high (more than 45 dB) because of the lack of mode-hopping noise resulting from the extremely short (less than 3 µm) external-cavity length and strong light feedback. These composite-cavity laser diode microdevices are fabricated on a gallium arsenide substrate to eliminate the need for optical alignment.

Resolution controllable optical time domain reflectometry based on low coherence interference

A low-coherence optical time domain reflectometer (OTDR) that can control spatial resolution is proposed to efficiently diagnose waveguides. This is achieved using a light source consisting of a superluminescent diode (SLD), an optical bandpass filter for truncating the SLD output, and an antireflection-coated laser diode booster amplifier. Two resolutions, 44 and 14 mu m, were experimentally demonstrated with and without the filter having a 2.7-nm full width at half maximum (FWHM), respectively. The length of the blind space and the minimum detectable reflectivity were respectively <7 mm and <-134 dB at a 3-Hz detection bandwidth, for both resolutions. The noise characteristics of the light source and the system performance are investigated theoretically and experimentally.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>