DFB Laser Diode Research Articles

A Silicon Platform With MEMS Active Alignment Function and Its Potential Application in Si-Photonics Packaging

A silicon (Si) platform, which consists of passive alignment structures (V-grooves), active microelectromechanical systems (MEMS) alignment components, mechanical locking mechanisms, and predeposited gold-tin soldering pads is developed to address the submicron accuracy assembly requirement of the discrete laser diode (LD) to a small core in-chip Si waveguide (WG). A 2-D in situ active alignment of a ball lens in LD-ball lens-Si-WG coupling system is presented here. The 1550-nm DFB LD and the passive Si-photonics chip are attached onto the platform, using flip-chip bonding process. The 2-D alignment of the ball lens is then achieved through the in-plane motion of the suspension arms and the specially designed V-groove. The position of the ball lens is subsequently fixed by the locking mechanism mechanically. MEMS electrothermal V-beam actuators, which can provide large force with a large displacement under a low driving voltage, i.e., >50 ?m at 25 V are employed in this platform. The effectiveness and stability of the arm locking function have been tested with a shift of <0.1 ?m after vibration testing (10g , 2 kHz). The integrated aligning and locking functions of the MEMS platform are also demonstrated through the LD-ball lens-Si-WG coupling system. These results show the potential of this MEMS platform in hybrid integrated Si photonics and applications that consist of LD-ball lens-Si-WG coupling system, e.g., the transmitter and transceiver.

An Efficient Solution to the Standing-Wave Approach Based on Cold Cavity Modes for Simulation of DFB Lasers

This paper describes an improved solution to the standing-wave model (SWM) based on cold cavity modes for simulating DFB laser diodes. It is found that the longitudinal carrier distribution has an opposite pattern from that of the photon distribution inside the laser cavity. An approximation to the carrier distribution is made under the moderate power assumption. This fact allows the integrals involved in the standing-wave formulation to be analytically performed beforehand and also leads to a great reduction to the number of carrier rate equations to be solved, consequently resulting in a more efficient solution to the previously proposed SWM.

Wide temperature operational range of a 1310 nm AlGaInAs MQW-DFB laser with silicon oxynitride as a facet coating

We successfully fabricated 1310 nm AlGaInAs MQW–DFB laser diodes with silicon oxynitride (SiON) as an AR facet coating. In this report, the low reflectivity of the single layer SiON film on the facet of the 1310 nm DFB LD is achieved, with the result that the FP mode can be effectively suppressed over a wide temperature range. The AlGaInAs MQWs is also adopted in order to achieve a good temperature performance of the 1310 nm DFB LD. We demonstrate that these devices have high slope efficiency, low threshold current, and high SMSR characteristics over the temperature range of −40 °C to 95 °C. Less than 1 dB degradation of slope efficiency was obtained when the temperature increased from 25 °C up to 95 °C. The side mode suppression ratio (SMSR) above 37 dB and clear openings of eye diagrams at 2.5 G modulation were maintained within the temperature range of −40 °C to 95 °C. These superior characteristics over the very wide temperature range of 1310 nm DFB laser diodes were achieved by the combination of AlGaInAs MQW and silicon oxynitride AR coating deposited on the facet.

Fiber‐based telecoms components at 1550 nm for the generation of cw‐THz by photomixing

AbstractA standard DFB diode laser operating at 1.55 μm has been used with an EDFA to construct a hybrid cw‐THz spectrometer. Frequency steps of as small as 4 MHz are demonstrated by current control whereas larger spectra in excess of 400 GHz have been realized using temperature control. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 991–994, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24207

A fiber bragg grating acceleration sensor interrogated by a DFB laser diode

A fiber Bragg grating (FBG) acceleration sensor interrogated by a DFB laser diode is demonstrated; the sensor is fabricated by packaging a FBG on to a cantilever; the interrogation scheme takes advantage of the intensity modulation of the narrow spectral bandwidth light of a distributed feedback laser diode, when the reflection spectrum curve of a FBG moves due to the strain which is applied on the sensor. The sensor’s response to the frequency and acceleration is measured by the experiment, and the factors which have an impact on the sensor’s sensitivity are also discussed.

Highly External Optical Feedback-Tolerant 1.49-$\mu$ m Single-Mode Lasers With Partially Corrugated Gratings

An InGaAsP single-mode laser diode (LD) highly tolerant to optical feedback was realized utilizing a partially corrugated grating with a window-mirror structure. The length and the coupling coefficient of the grating were properly chosen to enable moderate output power, low feedback sensitivity, and a side mode suppression ratio of 40 dB simultaneously. Under -16 dB external optical feedback, the relative intensity noise (RIN) was improved by 10 dB compared with that of a conventional DFB LD. The RIN was maintained at less than -120 dB/Hz under strong external optical feedback as high as -10 dB. These results show that the fabricated lasers are potentially useful for isolator-free optical modules.

Full-duplex radio-on-fiber transport systems based on main and multiple side modes injection-locked DFB laser diode

A full duplex radio-on-fiber (ROF) transport system based on main and multiple side modes injection-locked distributed feedback laser diode (DFB LD) is proposed and experimentally investigated. DFB LD is successfully injection-locked not only in the main mode but also in other side modes. A data signal of 70 Mbps/10 GHz (WiMAX) signal is transmitted over long-haul single-mode fiber (SMF) transmission. Good bit error rate (BER) performances were achieved for both down-link and up-link transmissions in our proposed full-duplex ROF transport systems.

Performance evaluation of a near infrared QEPAS based ethylene sensor

A sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) was evaluated for the detection of trace levels of ethylene at atmospheric pressure using a fiber coupled DFB diode laser emitting in the 1.62 µm spectral range. A noise-equivalent QEPAS signal of ∼4 ppm C2H4 was achieved for a 0.7 s data acquisition time using wavelength-modulation with a second-harmonic detection scheme on the strongest C2H4 absorption peak at 6177.14 cm−1 with an average optical power of ∼15 mW. Improved detection sensitivity of 0.5 and 0.3 ppm C2H4 (1σ) was demonstrated using longer averaging time of 70 and 700 s, respectively. Important characteristics for the QEPAS based sensor operation in real-world conditions are presented, particularly the influence of external temperature variations. Furthermore, the response time of the ethylene sensor was measured in different configurations and it is shown that the QEPAS technique can provide a response time in a few seconds range even without active gas flow.

Location of a time-varying disturbance using an array of identical fiber-optic interferometers interrogated by CW DFB laser

A novel technique for distributed detection and localization of vibrational disturbances is presented. It is based on a serial array of identical low-finesse Fabry-Perot interferometers interrogated at a fixed wavelength by DFB diode laser intensity modulated at 10 KHz. Interferometers are formed directly in the single mode SMF-28 fiber by pairs of fiber Bragg gratings with reflectivity < 0.05% each. A simple signal processing based on the Fourier transform of detected signals and evaluation of phases for different signal components enables localization of a perturbed interferometer with a high accuracy. In experiment, a localization accuracy of 10 meters has been demonstrated for 5 km long fiber after 1 s of averaging. The system has the capability of using well in excess of 100 interferometers in a single fiber channel. A simple sensor configuration and the use of low-frequency components make it potentially inexpensive and suitable for applications where a continuous monitoring of long structures has to be performed for appearance of vibrations.

Temperature and water concentration measurements in combustion gases using a DFB diode laser at 1.4 μm

A sensor using a single DFB diode laser at 1.4 μm based on wavelength modulation spectroscopy for the measurements of the gas temperature and the H2O concentration in combustion gases is developed. A line pair of H2O absorption transitions located at 7085.251 and 7085.876 cm−1 is selected based on some design rules. The 1f normalized 2f method is used to remove the need for the calibration and to correct for the transmission variation due to beam steering, mechanical misalignments, soot, and window fouling. The precision for the temperature and H2O concentration measurements are 1.05 and 2.10% in a controlled static cell, respectively. Burner experiments demonstrate the ability of the system for in situ measurements.

Fast all-optical flip-flop based on a single distributed feedback laser diode

Since there is an increasing demand for fast networks and switches, the electronic data processing imposes a severe bottleneck and all-optical processing techniques will be required in the future. All-optical flip-flops are one of the key components because they can act as temporary memory elements. Several designs have already been demonstrated but they are often relatively slow or complex to fabricate. We demonstrate experimentally fast flip-flop operation in a single DFB laser diode which is one of the standard elements in today's telecommunication industry. Injecting continuous wave light in the laser diode, a bistability is obtained due to the spatial hole burning effect. We can switch between the two states by using pulses with energies below 200 fJ resulting in flip-flop operation with switching times below 75 ps and repetition rates of up to 2 GHz.

Relative intensity noise measurements of 5 µm quantum cascade laser and 1.55 µm semiconductor laser

The magnitude of the relative intensity noise (RIN) of a 5 mum distributed-feedback quantum cascade laser (DFB-QCL) was compared with a conventional 1.55 mum DFB laser diode (LD). The RIN for the DFB-QCL at a frequency of 1 MHz was 157 dBm at 10 mW light output, about 5 dB higher than that of the DFB-LD, which could almost be fully explained by the semi-classical noise model. The resonant tunnelling induced noise, which might be a cause of the RIN degradation, was not observed.

Demonstration of saturation spectra of caesium D 2 line with a low linewidth distributed feedback laser diode

Low linewidths for Al-free active region distributed feedback lasers using a self-heterodyne measurement method (minimum beat width of 0.8 MHz at 20 mW and 12°C, 1.2 MHz at 852.12 nm 35 mW and 36°C) are demonstrated. Singlemode emission was achieved at 852.12 nm corresponding to the D2 caesium transition, with an optical output power of 35 mW at 140 mA under CW operation. Finally, the saturation spectra of caesium atoms with the DFB laser diode was recorded with a resolution close to the natural linewidth.

On the direct formation of HO2 radicals after 248 nm irradiation of benzene C6H6 in the presence of O2

We present in this work the direct observation of HO2 radicals after irradiation of benzene C6H6 at 248 nm in the presence of O2. HO2 radicals have been unambiguously identified using the very selective and sensitive detection of continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled to a laser photolysis reactor. HO2 radicals were detected in the first vibrational overtone of the OH stretch at 6638.20 cm-1, using a DFB diode laser. This reaction might be important because 248 nm photolysis of H2O2 has often been used in the past for studying the OH•-initiated degradation of C6H6, often using a large excess of C6H6 over H2O2. The possible importance of the title reaction with respect to these former laboratory studies has been quantified through comparison with HO2• signals obtained from 248 nm photolysis of H2O2: one obtains under our conditions (excess O2 and total pressure of 6.6 kPa helium) from the 248 nm irradiation of identical initial concentrations [C6H6]=[H2O2] the following relative initial radical concentrations: [HO2•]=(0.28±0.05)×[OH•]. Experiments with various O2 concentrations have revealed that the origin of the HO2 radicals is not the reaction of H-atoms with O2, but must originate from the reaction of O2 with excited C6H6*. The quantum yield of C6H6* formation has been deduced to ϕ=0.2±0.1.

High-Power Monolithic Two-Mode DFB Laser Diodes for the Generation of THz Radiation

We have devolved 1064 nm high-power monolithic distributed feedback lasers which operate simultaneously on two longitudinal modes. These modes correspond to the fundamental and first-order lateral mode and arise from a 7.5 mum width ridge waveguide supporting both of them. They are further stabilized by a first-order grating built into an InGaP/GaAs/InGaP multilayer structure. The threshold current of the laser is 66 mA, the slope efficiency is 0.5 W/A, and an output power of ~500 mW is reached. Detailed investigations of the intensity distribution of lateral and vertical far fields and the spectral behavior are shown. The longitudinal mode spacing at 260 mW is 0.56 nm corresponding to approximately 150 GHz. THz generation is demonstrated by mixing the two-line laser emission in a LT-GaAsSb photomixer.

All-optical flip-flops based on DFB laser diodes and DFB-arrays

We present numerical and experimental results on a number of different all-optical flip-flops which are based on DFB laser diodes or DFB-arrays. All these flip-flop concepts show potential for fast switching with low switching energy and high extinction ratio. They are moreover very robust in the sense that the switching pulses (and the injected CW beam in some cases) can be of arbitrary wavelength and that the bistability characteristics can be tuned by simple variation of the current injected into the devices. Two different designs for all-optical flip-flop operation will be discussed in detail. The first one is a DFB or DBR laser diode coupled to a semiconductor optical amplifier, in which the bidirectional coupling between laser and amplifier causes the bistability. The second concept is based on bistable behaviour in a single AR-coated DFB laser, with low coupling coefficient and in which a CW signal is injected. These all-optical flip-flops can easily be extended to optically switchable multistate devices with any number of stable states. Such multistate devices are briefly discussed at the end.

The near-infrared (1.30–1.70 μm) absorption spectrum of methane down to 77 K

The high resolution absorption spectrum of methane has been recorded at liquid nitrogen temperature by direct absorption spectroscopy between 1.30 and 1.70 microm (5850-7700 cm(-1)) using a newly developed cryogenic cell and a series of DFB diode lasers. The investigated spectral range includes part of the tetradecad and the full icosad regions for which only very partial theoretical analysis are available. The analysis of the low temperature spectrum will benefit from the reduction of the rotational congestion and from the narrowing by a factor of 2 of the Doppler linewidth allowing the resolution of a number of multiplets. Moreover, the energy value and rotational assignment of the angular momentum J of the lower state of a given transition can be obtained from the temperature variation of its line intensity. This procedure is illustrated in selected spectral regions by a continuous monitoring of the spectrum during the cell cool-down to 77 K, the temperature value being calculated at each instant from the measured Doppler linewidth. A short movie showing the considerable change of a spectrum during cool-down is attached as Supplementary Material. The method applied to a 30 cm(-1) section of the tetradecad spectrum around 6110 cm(-1) has allowed an unambiguous determination of the J values of part of the observed transitions.

The near infrared spectrum of ozone by CW-cavity ring down spectroscopy between 5850 and 7000 cm−1: new observations and exhaustive review

Weak vibrational bands of (16)O(3) could be detected in the 5850-7030 cm(-1) spectral region by CW-cavity ring down spectroscopy using a set of fibered DFB diode lasers. As a result of the high sensitivity (noise equivalent absorption alpha(min) approximately 3 x 10(-10) cm(-1)), bands reaching a total of 16 upper vibrational states have been previously reported in selected spectral regions. In the present report, the analysis of the whole investigated region is completed by new recordings in three spectral regions which have allowed: (i) a refined analysis of the nu(1) + 3nu(2) + 3nu(3) band from new spectra in the 5850-5900 cm(-1) region; (ii) an important extension of the assignments of the 2nu(1)+5nu(3) and 4nu(1) + 2nu(2) + nu(3) bands in the 6500-6600 cm(-1) region, previously recorded by frequency modulation diode laser spectroscopy. The rovibrational assignments of the weak 4nu(1) + 2nu(2) + nu(3) band were fully confirmed by the new observation of the 4nu(1) + 2nu(2) + nu(3)- nu(2) hot band near 5866.9 cm(-1) reaching the same upper state; (iii) the observation and modelling of three A-type bands at 6895.51, 6981.87 and 6990.07 cm(-1) corresponding to the highest excited vibrational bands of ozone detected so far at high resolution. The upper vibrational states were assigned by comparison of their energy values with calculated values obtained from the ground state potential energy surface of (16)O(3). The vibrational mixing and consequently the ambiguities in the vibrational labelling are discussed. For each band or set of interacting bands, the spectroscopic parameters were determined from a fit of the corresponding line positions in the frame of the effective Hamiltonian (EH) model. A set of selected absolute line intensities was measured and used to derive the parameters of the effective transition moment operator. The exhaustive review of the previous observations gathered with the present results is presented and discussed. It leads to a total number of 3863 energy levels belonging to 21 vibrational states and corresponding to 7315 transitions. In the considered spectral region corresponding to up to 82% of the dissociation energy, the increasing importance of the "dark" states is illustrated by the occurrence of frequent rovibrational perturbations and the observation of many weak lines still unassigned.

Antimonide-based lasers and DFB laser diodes in the 2–2.7 μm wavelength range for absorption spectroscopy

We report on Fabry–Perot semiconductor lasers and single frequency distributed feedback lasers based on GaInAsSb/AlGaAsSb quantum wells. The laser structures were grown by molecular beam epitaxy on GaSb substrates. The devices were etched either by wet process or by inductively coupled plasma (ICP) process. Electron-beam lithography was used to deposit a metal Bragg grating on each side of the laser ridge to fabricate the DFB lasers. The devices all operate in the continuous wave regime at room temperature with a single frequency emission above 2.6 μm and good tuning properties, making them well adapted to tunable diode laser absorption spectroscopy.

Distributed Feedback Laser Using Buried Dielectric Grating

In this paper, we report a DFB laser diode with a buried SiO2 grating. Epitaxy lateral overgrowth by metalorganic chemical vapour deposition (MOCVD) is conducted to grow the p-type InP cladding layers in the nano-patterned dielectric grating template. The large refractive index difference between SiO2 and InP results an index coupling coefficient κ of about 250 cm-1. The fabricated DFB laser showed a side mode suppression ratio larger than 45 dB measured. The technology developed can also be used for other applications that require high efficiency grating structure.