Distributed Feedback Diode Research Articles

Dependence of Er:Yb-codoped 15μm amplifier on wavelength-tuned auxiliary seed signal at 1μm wavelength

We report on experiments performed with a cladding-pumped single-mode Er:Yb-codoped single-frequency fiber amplifier simultaneously seeded by a distributed-feedback diode at 1556 nm and a tunable external-cavity diode laser emitting at a wavelength of about 1 μm wavelength. The influence of the output wavelength of the external-cavity laser on amplification and reabsorption behavior of the Yb emission as well as the amplifier performance at a wavelength of 1556 nm is examined experimentally.

Phase-locking of the beat signal of two distributed-feedback diode lasers to oscillators working in the MHz to THz range

We present difference-frequency stabilization of free-running distributed-feedback (DFB) diode lasers, maintaining a stable phase-lock to a local oscillator (LO) signal. The technique has been applied to coherent hybrid THz imaging which employs a high-power electronic radiation source emitting at 0.62 THz and electro-optic detectors. The THz radiation of the narrow-band emitter is mixed with the difference frequency of the DFB diode laser pair. The resulting intermediate frequency is phase-locked to the LO signal from a radio-frequency generator using a fast laser-current control loop. The stabilization scheme can be adapted readily to a wide range of applications which require stabilized laser beat-notes.

Highly accurate Michelson type wavelength meter that uses a rubidium stabilized 1560 nm diode laser as a wavelength reference

We investigated the accuracy limitation of a wavelength meter installed in a vacuum chamber to enable us to develop a highly accurate meter based on a Michelson interferometer in 1550 nm optical communication bands. We found that an error of parts per million order could not be avoided using famous wavelength compensation equations. Chromatic dispersion of the refractive index in air can almost be disregarded when a 1560 nm wavelength produced by a rubidium (Rb) stabilized distributed feedback (DFB) diode laser is used as a reference wavelength. We describe a novel dual-wavelength self-calibration scheme that maintains high accuracy of the wavelength meter. The method uses the fundamental and second-harmonic wavelengths of an Rb-stabilized DFB diode laser. Consequently, a highly accurate Michelson type wavelength meter with an absolute accuracy of 5 x 10(-8) (10 MHz, 0.08 pm) over a wide wavelength range including optical communication bands was achieved without the need for a vacuum chamber.

Investigations of various cw terahertz photomixers

Various cw terahertz (THz) photomixers were investigated and compared. Beams of two cw, tunable, single mode DFB (distributed feedback) diode lasers were used for illumination of the devices. Simple photoexcited gap structure, spiral-type and dipole-type integrated antennae patterns photomixers were used while carrying out investigations. Cw THz radiation has been generated by photoconductive devices made using low-temperature-grown GaAs layers. Antennae fabricated on GaAs and GaBiAs layers were used for coherent detection of cw THz radiation. It was obtained that the sensitivity of GaBiAs detectors is more than two times higher than in the case of GaAs detectors. GaAs emitters with integrated spiral-type antennae were most efciently emitting in the low frequency range; enhanced bias voltages of such devices result in generated THz power comparable with the photomixers with interdigitated contact structures.

Experimental Investigation of Chaos Synchronization in DFB Diode Lasers with Unsymmetrical Scheme

We experimentally generate high dimension chaotic waveforms with smooth spectrum using a distributed feedback (DFB) semiconductor laser with unidirectional fibre ring long-cavity feedback, and implement the stable chaos synchronization when the chaotic light is injected into a solitary DFB laser diode. The synchronization quality is investigated by time-domain and frequency-domain analysis separately. The frequency-domain analysis indicates that the synchronization has higher quality in the high frequency band. The influences of the injection strength and the frequency detuning on the synchronization are measured. Our experimental results show that the robust synchronization can be maintained with the optical frequency detuning from -UGHz to 40 GHz.

Testing carbon sequestration site monitor instruments using a controlled carbon dioxide release facility

Two laser-based instruments for carbon sequestration site monitoring have been developed and tested at a controlled carbon dioxide (CO(2)) release facility. The first instrument uses a temperature tunable distributed feedback (DFB) diode laser capable of accessing the 2.0027-2.0042 microm spectral region that contains three CO(2) absorption lines and is used for aboveground atmospheric CO(2) concentration measurements. The second instrument also uses a temperature tunable DFB diode laser capable of accessing the 2.0032-2.0055 mum spectral region that contains five CO(2) absorption lines for underground CO(2) soil gas concentration measurements. The performance of these instruments for carbon sequestration site monitoring was studied using a newly developed controlled CO(2) release facility. A 0.3 ton CO(2)/day injection experiment was performed from 3-10 August 2007. The aboveground differential absorption instrument measured an average atmospheric CO(2) concentration of 618 parts per million (ppm) over the CO(2) injection site compared with an average background atmospheric CO(2) concentration of 448 ppm demonstrating this instrument's capability for carbon sequestration site monitoring. The underground differential absorption instrument measured a CO(2) soil gas concentration of 100,000 ppm during the CO(2) injection, a factor of 25 greater than the measured background CO(2) soil gas concentration of 4000 ppm demonstrating this instrument's capability for carbon sequestration site monitoring.

Photoacoustic CO2 sensor based on a DFB diode laser at 2.7 μm

We present a new detection scheme for carbon dioxide (CO2) based on a custom-made room temperature distributed feedback (DFB) diode laser at 2.7 μm, currently representing one of the lasers with the highest emission wavelength of its kind. The detector's especially compact and simple set-up is based on photoacoustic spectroscopy (PAS). This method makes use of the transformation of absorbed modulated radiation into a sound wave. The sensor enables a very high detection sensitivity for CO2 in the ppb range. Furthermore, the carefully selected spectral region as well as the narrow bandwidth and wide tunability of the single-mode laser ensure an excellent selectivity. Even measurements of different CO2 isotopes can be easily performed. This enables applications in industrial sensing and medical diagnostics (e.g. 13C-breath tests).

First demonstration of a high performance difference frequency spectrometer on airborne platforms

We discuss the first airborne deployment and performance tests of a mid-IR difference frequency spectrometer system for highly sensitive measurements of formaldehyde. The laser system is based upon difference-frequency generation (DFG) at ~3.5 mum by mixing a DFB diode laser at 1562 nm and a distributed feedback (DFB) fiber laser at 1083 nm in a periodically poled LiNbO(3) (PPLN) crystal. Advanced LabVIEW software for lock-in, dual-beam optical noise subtraction, thermal control and active wavelength stabilization, renders a sensitivity of ~20 pptv (Absorbance ~7*10(-7)) for 30s of averaging. The instrument's performance characteristics spanning more than 300 flight hours during three consecutive airborne field missions MIRAGE, IMPEX and TexAQS operating on two airborne platforms, NCAR's C-130 and NOAA's P-3 aircraft are demonstrated.

Looking into the volcano with a Mid-IR DFB diode laser and Cavity Enhanced Absorption Spectroscopy

We report on the first application of extended-wavelength DFB diode lasers to Cavity-Enhanced Absorption Spectroscopy in-situ trace measurements on geothermal gases. The emission from the most active fumarole at the Solfatara volcano near Naples (Italy) was probed for the presence of CO and CH(4). After passing through a gas dryer and cooler, the volcanic gas flow (98% CO(2)) was analysed in real time for the concentration of these species, whose relatively strong absorption lines could be monitored simultaneously by a single Distributed Feed-Back (DFB) GaSb-based diode laser emitting around 2.33 mum (4300 cm(-1)) at room temperature. The concentrations were found to be about 3 ppm and 75 ppm, respectively, while actual detection limits for these molecules are around 1 ppb. We discuss the possibility of detecting other species of interest for volcanic emission monitoring.

Frequency stabilization of a frequency-doubled 197.2 THz distributed feedback diode laser on rubidium 5S 1/2→7S 1/2 two-photon transitions

A 197.2 THz (1520.2 nm) ITU-T grid distributed feedback (DFB) diode laser is frequency stabilized at 197.198 THz by 1ocking its second harmonic (SH) signal on the rubidium 5S 1/2→7S 1/2 two-photon transition at 394.396 THz (760.1 nm). With 100 mW from the DFB diode laser and amplifying by an erbium-doped fiber amplifier, we obtain an SH power of 15 mW using a periodically poled lithium niobate (PPLN) waveguide frequency doubler. The stability was 2×10 −11 (10 s), corresponding to a frequency variation of 4 kHz at 1520.2 nm. Our scheme provides a compact and high performance frequency reference in the communication band.

Relative line intensity measurement in absorption spectra using a tunable diode laser at 1.6 μm: application to the determination of 13CO2/12CO2 isotope ratio

The measurement of relative intensities in CO2 combination bands spectrum is performed using wavelength modulation spectroscopy (WMS) and a DFB (distributed feedback) diode laser operating at 1.6 μm. The diode laser is stabilized with an external Fabry–Perot interferometer and absorption spectroscopy is performed in a multipass gas cell. A spectrum containing spectral lines of both 13CO2 and 12CO2 isotopic species is recorded. The variation of laser power during frequency scanning and the line shape are taken into account to accurately extract line intensities from experimental data. The isotopic concentration ratio is deduced from the intensity ratio. Both ratios are measured with an accuracy of about 0.5% in pure CO2.

Passive optical network for microcellular CDMA personal communication service

We propose and demonstrate a fiber-optic network for microcellular code-division multiple access (CDMA) personal communication service. The proposed network is based on a passive double-star architecture. The relaxed dynamic range requirements of CDMA signals allowed the use of double-star architecture. The proposed network was demonstrated by using various light sources [distributed-feedback lasers, Fabry-Perot (FP) lasers, and light-emitting diodes (LED's)] to examine the possibility of using inexpensive components. The result shows that this network could be implemented cost-effectively by using a FP laser for the downlink and LED's for the uplink.

Carrier transport effects in long-wavelength multiquantum-well lasers under large-signal modulation

Significant differences are observed between long-wavelength multiquantum-well (MQW) and bulk distributed-feedback (DFB) diode lasers in terms of their gain-switched dynamic performance. Through careful comparison of experimental and theoretical results, carrier transport is found to be particularly important in determining gain-switched operation. >

Single-heterostructure distributed-feedback GaAs-diode lasers

This paper reports the fabrication, testing, and analysis of distributed-feedback (DFB) single-heterostructure (SH) electrically pumped GaAs lasers. The techniques of fabricating the DFB grating and diode using interferometric exposure of photoresist, development, ion milling, liquid-phase-epitaxial growth, and diffusion are described in detail. Next, experimental results on a variety of diodes operating at 77 K are presented. It is shown that narrow laser linewidth (< 0.15 Å) and low threshold operation (775 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) can be obtained. Also reported is output coupling from the grating which results in highly collimated laser beams with divergence of approximately 0.35°. Coupling coefficients, which determine laser threshold, are computed as a function of device parameters including physical dimensions, refractive indices, grating size and shape, and Bragg order for single-and double-heterostructure geometries. Calculated and measured thresholds are shown to be in good agreement.