YAG Ring Laser Research Articles

Experimental relative frequency stabilization of a set of lasers using optical phase-locked loops

A relative frequency stabilization technique using optical phase locking of miniature diode pumped Nd:YAG ring lasers is described. The master laser is RF phase modulated with a modulation index up to 7.4, and slave lasers are locked up to 21 master laser sidebands with a frequency stability better than 3 kHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

560 Mb/s optical PSK synchronous heterodyne experiment

A phase-locked optical heterodyne receiver constructed using a 1320-nm diode-pumped miniature Nd:YAG ring laser is discussed. Using this receiver and a transmitter based on another Nd:YAG laser, a 560-Mb/s phase-shift keying (PSK) synchronous heterodyne transmission was demonstrated over 78 km of single-mode fiber. With an optical phase-locked loop (PLL) natural frequency of 32 kHz and a damping factor of 1.46, the receiver sensitivity, measured at the output of the transmission link, was -48.7 dBm, or 159 photons/b. The corresponding detected sensitivity, measured on the surface of the p-i-n diode, was -51.8 dBm or 78 photons/b. This result suggests that the receiver sensitivity would have been about 82 photons/b if a balanced receiver with 0.2-dB excess coupler loss had been used. The impact of the finite intermediate frequency (IF) on heterodyne system performance was investigated; it was found that an IF of at least twice the bit rate is needed for a negligibly small penalty.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An optical PSK homodyne transmission experiment using 1320 nm diode-pumped Nd:YAG lasers

A second-order optical phase-locked loop was constructed using 1320-nm diode-pumped miniature Nd:YAG ring lasers. Using the loop, a 140-Mb/s PSK homodyne transmission experiment was demonstrated over 28.6 km of single-mode fiber. With a loop natural frequency of 13 kHz and a damping factor of 0.6, the receiver sensitivity was -62.8 dBm, or 25 photons/bit. The authors believe this is the highest sensitivity obtained to date with any optical communication system. >

Optical generation, distribution, and control of microwaves using laser heterodyne

Demonstrated is the optical generation and transmission of a microwave signal by the mixing of two high-quality optical signals from diode-laser-pumped Nd:YAG ring lasers, resulting in a narrow microwave line width (less than 5 kHz line width at 3 dB and less than -115 dBc/Hz at 300 kHz from line center) and broad microwave tunability (DC to 52 GHz). A III-V semiconductor waveguide with a doping superlattice active region is used to optoelectronically provide 20 dB of amplitude control and up to 5 pi of phase shift. This approach can be straightforwardly implemented using integrated optics and fiberoptic links for control of phased-array antenna elements. >

Two-piece, piezoelectrically tuned, single-mode Nd:YAG ring laser

A two-piece, single-mode, piezoelectrically tuned Nd:YAG ring laser has been demonstrated at 1338 nm. The laser was derived from a previously demonstrated monolithic unidirectional ring laser that has been cut in two to allow the cavity to be tuned by varying the gap between the two pieces. More than 1 mW of output power was produced when the laser was pumped by a 30-mW, 809-nm GaAlAs semiconductor laser. Continuous tuning over the 13.5-GHz longitudinal mode spacing with millisecond sweep times was demonstrated.

A single frequency Nd:YAG ring laser pumped by laser diodes

The design and operation of a diode-pumped Nd:YAG ring laser is described. The laser is shown to be a highly versatile device, capable of efficient generation of both the fundamental and second harmonic frequencies, CW and Q-switched. Single-frequency outputs in excess of 540 mW at 1.06 μm and 18.9 mW at 532 nm output were obtained, whereas multi-longitudinal mode Q-switched operation produced 22.4 μJ per pulse at 5 kHz in the fundamental and 7.3 μJ power pulse at 532 nm.

Miniature Nd:YAG lasers: noise and modulation characteristics

The frequency and intensity noise spectra, as well as the frequency modulation (FM) response, of 1320-nm laser-diode-pumped miniature Nd:YAG ring lasers have been measured. The frequency noise spectrum has a resonance peak at the relaxation oscillation frequency of the laser (between 123 and 150 kHz) and is flat beyond 200 kHz with a spectral density of 613 rad/sup 2/-Hz, much smaller than that of semiconductor lasers; the corresponding laser linewidth is less than 49 Hz. The relative intensity noise is -140 dB/Hz at the valley and has a resonance peak at the relaxation oscillation frequency of the laser. The FM response is flat from DC to 110 kHz and is in the 0.65-3 MHz/V range; the modulation frequency is limited by the relaxation oscillation frequency of the laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

565 Mbit/s optical DPSK and PSK heterodyne transmission experiment using Nd:YAG lasers at 1.3 μm

A 565 Mbit/s optical DPSK and PSK transmission experiment is described. Stable monolithic Nd:YAG ring lasers were used as light sources. A PSK demodulation scheme achieved a receiver sensitivity of −53.4 dBm and was found to be l.3 dB better than DPSK.

Single frequency Q-switched operation of a laser dipole-pumped, Nd: YAG ring laser

We describe unidirectional, single frequency, Q-switched operation of a laser diode-pumped, non-monolithic, Nd: YAG ring laser. We have obtained pulse energies of 20 μJ and 18 ns duration, corresponding to a peak power of approximately 1 kW at a repetition rate of 500 Hz.

Injection locking of a 13-W cw Nd:YAG ring laser

A lamp-pumped, 13-W cw Nd:YAG ring laser at 1.064 microm is injection locked using a 40-mW single-frequency diodelaser-pumped Nd:YAG laser as the master oscillator. The phase fidelity of the injected slave to the master is measured using an all-optical technique.

Frequency fluctuations of a diode-pumped Nd:YAG ring laser

We have measured the spectral density of the frequency fluctuations of a diode-pumped single-mode monolithic Nd:YAG ring aser by locking a Fabry-Perot resonator to the laser frequency. The fluctuations approach the limit due to spontaneous emission (the Schawlow-Townes limit) at frequencies above 80 kHz. The inherent frequency stability of these lasers makes them attractive as a potential light source for gravitational-wave interferometers.

Interferometric measurement of low-frequency phase noise characteristics of diode laser-pumped Nd:YAG ring laser

We report the interferometric measurement of the phase noise characteristics of a diode laser-pumped solid-state Nd:YAG 1.3μ laser based on a nonplanar ring cavity. Results show that the device has a low-frequency phase noise approximately three orders of magnitude lower than that observed with semiconductor diode lasers. The use of this source in fibre sensing applications is discussed.

Optical receiver and modulator frequency response measurement with a Nd:YAG ring laser heterodyn technique

A description is given of how the frequency response of optical receivers can be accurately calibrated by measuring a heterodyne signal generated by mixing two Nd:YAG ring lasers. One laser signal passes through the modulator while the other functions as a local oscillator to convert one of the sidebands of the modulated carrier to a fixed intermediate signal. This heterodyne system offers more than 50 dB of dynamic range. Calibration of both optical phase and amplitude modulators is achieved. The technique presented eliminates the need for a high-speed photoreceiver, has a good signal-to-noise ratio, and makes measurement of phase modulator frequency response possible. >

Fast frequency tuning and phase locking of diode-pumped Nd:YAG ring lasers

We have built a diode-pumped single-mode monolithic Nd:YAG ring-laser oscillator that can be tuned piezoelectrically over several tens of megahertz in a few microseconds. Frequency stability over 1 msec is better than 500 Hz. We have electronically phase locked two lasers for periods of minutes with phase noise of 29 mrad rms.

Studies of the coherence properties of a diode-pumped Nd:YAG ring laser

The coherence properties of a diode-pumped Nd:YAG ring laser have been studied by a self-heterodyne autocorrelation technique using a very long path difference Mach–Zehnder interferometer and by homodyne interferometry in a Michelson interferometer. Results show the laser to have a linewidth of Δf=6.1±0.7 kHz at a power output of 5 mW.

Coherent summation of injection-locked, diode-pumped Nd:YAG ring lasers

A binary grating has been used to achieve coherent summation of diode-laser-pumped Nd:YAG ring lasers operating at 1.06 μm. Mutual coherence of two such devices was achieved by optical injection locking. This is believed to be the first demonstration of cw injection locking of solid-state lasers other than semiconductor diode lasers. By combining two beams, an efficiency of 75% (92% of the theoretical limit) has been demonstrated in a configuration that could be used to combine a large number of individual lasers.

Unidirectional diode-laser-pumped Nd:YAG ring laser with a small magnetic field

Single-mode operation of a monolithic semiconductor-laser-pumped unidirectional ring Nd:YAG laser has been demonstrated at 1319 and 1338 nm. The ring design optimizes the polarization eigenvalue difference between counterpropagating modes of the ring. The laser threshold is 4.5 mW, and the magnetic-field requirement for unidirectional operation is approximately 100 G.

Continuous-wave garnet ring laser emitting single-mode linearly polarized radiation and intracavity second harmonic generation in LiIO3

An investigation was made of a method of selecting the TEM00 mode in a laser by using birefringence induced in an active element during pumping. The reasons for astigmatism of the thermal lens in an active element with Brewster-cut faces were determined and an investigation was made of the structure of the radiation field of a laser using such an element. It is found that the optimal conditions for efficient emission of linearly polarized radiation in the dominant transverse mode in a laser with a Brewster active element are achieved by using an active element of rectangular cross section with a specific ratio of the sides. A prototype YAG ring laser emitting linearly polarized radiation with a power of 15 W in the TEM00, mode is described. By using an LiIO3 nonlinear element, 0.43 W of cw radiation at the 0.53 μ wavelength is obtained.