DBR Section Research Articles

THE INFLUENCE OF A RESIDUAL REFLECTIVITY AT THE FRONT FACET OF A MULTISECTION MASTER-OSCILLATOR POWER-AMPLIFIER

This paper reports on the theoretical end experimental investigation of the output characteristics of a multisection master-oscillator power-amplifier (MOPA). It consists of a master oscillator (MO) composed by a gain section surrounded by two DBR sections monolithically integrated with a power amplifier (PA). We use a traveling wave equation model to calculate the optical output power in dependence on the current injected into the PA. The experimental results can be well explained with our theoretical analysis. For a finite front facet reflectivity of the PA the system is acting as a compound cavity.

Electroabsorption modulator‐integrated distributed Bragg reflector laser diode for C‐band WDM‐based networks

AbstractWe report an electroabsorption modulator (EAM)‐integrated distributed Bragg reflector laser diode (DBR‐LD) capable of supporting a high data rate and a wide wavelength tuning. The DBR‐LD contains two tuning elements, plasma and heater tunings, both of which are implemented in the DBR section, which have blue‐shift and red‐shift in the Bragg wavelength through a current injection, respectively. The light created from the DBR‐LD is intensity‐modulated through the EAM voltage, which is integrated monolithically with the DBR‐LD using a butt–joint coupling method. The fabricated chip shows a threshold current of approximately 8 mA, tuning range of greater than 30 nm, and static extinction ratio of higher than 20 dB while maintaining a side mode suppression ratio of greater than 40 dB under a window of 1550 nm. To evaluate its modulation properties, the chip was bonded onto a mount including a radiofrequency line and a load resistor showing clear eye openings at data rates of 25 Gb/s nonreturn‐to‐zero and 50 Gb/s pulse amplitude modulation 4‐level, respectively.

16-channel tunable and 25-Gb/s EAM-integrated DBR-LD for WDM-based mobile front-haul networks.

We report a tunable distributed Bragg reflector-laser diode (DBR-LD) integrated with an electro-absorption-modulator (EAM) at an operating wavelength of 1.3 µm. This LD consists of gain, phase control (PC), DBR, and EAM sections, realized by using a butt-coupling technique in monolithically integrating the multiple quantum wells (MQWs) with the passive core and by applying an etched-mesa buried hetero-structure (EMBH) to the resonance cavity (i.e., gain to DBR section) and a deep-ridge type to the EAM section in fabricating the waveguide structure. Wavelength tuning of the LD is achieved by both applying a voltage to the heater metal of DBR section (coarse tuning) and injecting a current to the ohmic metal of PC section (fine tuning). From the work, the fabricated chips show a threshold current of about 13 mA, a side mode suppression ratio (SMSR) of more than 35 dB, and a tuning range of 15 nm within a heater voltage of 2 V. Dynamic tests for the EAM-integrated LD show the 3 dB bandwidth of more than 20 GHz and clear 25 Gb/s eye openings with a dynamic extinction ratio (DER) of over 7 dB for 16 channels spaced at the wavelength interval of 0.55 nm. Based on these results, we conclude that the EAM-integrated DBR-LD is capable of providing 16 channel operation at a data rate of 25 Gb/s and can be used as an effective light source for WDM-based mobile front-haul networks.

1.3-µm and 10-Gbps tunable DBR-LD for low-cost application of WDM-based mobile front haul networks.

We report a 1.3-µm and 10-Gbps tunable distributed Bragg reflector laser diode (DBR-LD) for the low-cost application of a wavelength division multiplex based mobile front-haul network. The device consists of gain, phase control, and DBR sections, implemented using a butt-coupling method through a monolithic integration and through the introduction of an etched mesa planar buried hetero-structure in a waveguide structure. From the work, a 560-µm long DBR-LD with a 220-µm long micro-heater DBR section has a threshold current of 10 mA ± 1 mA and a tuning range of more than 15 nm within a heater injection current of ∼100 mA. Spectral and dynamic tests for this LD show 16 channels spaced a wavelength grid of 0.8 nm with a side mode suppression ratio of greater 40 dB and clear eye openings with a dynamic extinction ratio of over 5.4 dB at an operating current of 60 mA.

Proposal of novel structure for wide wavelength tuning in distributed Bragg reflector laser diode with single grating mirror

We report a novel structure that is capable of wide wavelength tuning in the distributed Bragg reflector laser diode (DBR-LD) with a single grating mirror. This device's DBR section has two tuning elements, plasma, and heater tunings, which are implemented simultaneously on the top of a single waveguide by using an in-between dielectric layer. For the proposed structure, a three-dimensional thermal simulation was conducted. The results showed that the temperature profile within the waveguide is highly affected by the position of heater metal and thermal conductivity of the p-cladding layer. As a result, it is important to use a uniform temperature region in the DBR section for a wide tuning range and stable single-mode operation. For a 550-μm long DBR-LD with a 250-μm long DBR section, a tuning range of 26 nm (i.e., 7 nm for plasma tuning and 19 nm for heater tuning); an SMSR of more than 45 dB; and a peak power variation of less than ± 2.5 dB were obtained. From the comparisons of two DBR-LDs with only one tuning element, we confirmed that using the dielectric layer is a very effective way of achieving a wide tuning under the independent tuning operation.

Performance of Widely Tunable Multi-Quantum-Well and Bulk Laser Diodes and the Main Limiting Factors

The output power and tuning performance of multi-quantum-well (MQW) and bulk InGaAsP/InP-distributed Bragg reflector (DBR) tunable laser diodes (TLDs) are investigated over a wide wavelength tuning range using physics-based PICS3D and VPI laser simulation tools within the travelling-wave formalism. The key result of our simulations is the discovery of a new effect in TLDs due to intervalence band absorption (IVBA) in passive phase and DBR sections, which limits the wavelength tuning range. The physical mechanism responsible for such a behavior is a collapse of the spectral-mode selectivity by the DBR due to large IVBA losses in the phase or/and DBR sections. We fundamentally demonstrate different roles played by the IVBA in the active and passive sections of a TLD. It is shown that the IVBA in passive sections and the carrier relaxation broadening (CRB) of the Lorentzian lineshape function in the lasers’ active and passive sections play a crucial role in TLD tuning operation. The IVBA coefficient $\text{k}_{\mathrm {IVBA}}$ and the intraband relaxation time $\tau _{in}$ are the major limiting factors that define the output power variation and the achievable tuning range of the lasers. Both bulk and MQW lasers with small $\text{k}_{\mathrm {IVBA}}$ demonstrate a wide wavelength tuning range above 30 nm, while for large $\text{k}_{\mathrm {IVBA}}$ , the tuning range drops below 10 nm. We show that the output power variation with tuning due to the CRB parameter $\tau _{in}$ is qualitatively different in bulk and MQW TLDs. The TLD tuning and power performance is also strongly affected by the shapes of the net gain and the cavity mirror loss spectra and their mutual positioning with respect to the lasing cavity mode during the tuning. The limiting parameters $\text{k}_{\mathrm {IVBA}}$ and $\tau _{in}$ as well as gain and mirror loss spectra must be thoroughly evaluated in each TLD structure prior to the device design and optimization in order to achieve the best performance in terms of the wavelength tuning and the output power stability.

Fast Tuneable InGaAsP DBR Laser Using Quantum-Confined Stark-Effect-Induced Refractive Index Change

We report a monolithically integrated InGaAsP DBR ridge waveguide laser that uses the quantum-confined Stark effect (QCSE) to achieve fast tuning response. The laser incorporates three sections: a forward-biased gain section, a reverse-biased phase section, and a reverse-biased DBR tuning section. The laser behavior is modeled using transmission matrix equations and tuning over ~8 nm is predicted. Devices were fabricated using post- growth shallow ion implantation to reduce the loss in the phase and DBR sections by quantum well intermixing. The lasing wavelength was measured while varying the reverse bias of the phase and DBR sections in the range 0 V to <-2.5 V. Tuning was noncontinuous over a ~7-nm-wavelength range, with a side-mode suppression ratio of ~20 dB. Coupled cavity effects due to the fabrication method used introduced discontinuities in tuning. The frequency modulation (FM) response was measured to be uniform within plusmn2 dB over the frequency range 10 MHz to 10 GHz, indicating that tuning times of 100 ps are possible.

Low-threshold and high-efficiency operation of 1.5 µm distributed reflector laser with DFB grating and Q-wire DBR sections

A low-threshold and high-efficiency distributed reflector laser consisting of active distributed feedback and quantum-wire distributed Bragg reflector sections has been demonstrated. A threshold current Ith as low as 2.5 mA ( jth=190 A/cm2), an external differential quantum efficiency from the front facet of 36%, and a submode suppression ratio of 54 dB at a bias current of twice the threshold current were obtained for an active section length of 300 µm with a stripe width of 4.4 µm.

Analysis of surface-emitting second-order distributed feedback lasers with central grating phaseshift

An analysis of second-order distributed feedback lasers (DFB) with central grating phaseshift is performed. The devices have an active grating (i.e., DFB) section, passive grating sections (i.e., DBRs); and the active grating is formed at a metal-semiconductor interface. Coupled-mode theory and the transfer matrix method are employed. It is found that a central grating phaseshift, /spl Delta//spl phi/, of 180/spl deg/ causes the laser to radiate in a beam of symmetric near-field amplitude profile, in sharp contrast to conventional second-order DFB lasers which radiate in beams of asymmetric near-field amplitude profile. In turn the far-field profile becomes a single-lobe beam pattern. Thus, a means to fundamentally obtain surface emission in an orthonormal single-lobe beam from a second-order DFB/DBR device has been found. The orthornomal-beam emission is achieved at no penalty in device efficiency. External differential quantum efficiencies, /spl eta//sub d/, in excess of 70% can be obtained, and the guided-field intensity profile is substantially uniform. The effects of the lengths of the DFB section (L/sub DFB/) and of each of the DBR sections (L/sub DBR/) on device performance are analyzed and optimal values are found to occur for L/sub DFB/ in the 500-700 /spl mu/m range and for L/sub DBR/ in the 600-700 /spl mu/m range. One can obtain /spl eta//sub D/ values as high as 76% from devices with 80% of the energy in the central lobe, and moderate threshold gains (i.e., 40 cm/sup -1/). Threshold gains as low as 25 cm/sup -1/ can also be obtained from highly efficient devices (i.e., /spl eta//sub D//spl cong/70%), at some penalty in guided-field uniformity. In either case the intermodal discrimination is quite high (70-75 cm/sup -1/). Gratings with half-wave (i.e., /spl pi/) phaseshifts have been fabricated by using the dual-tone photoresist method, and the concept has been experimentally proven: orthonormal, single-lobe emission in a diffraction-limited beam from 1500 /spl mu/m-long devices. Extension to two-dimensional (2-D) large-aperture: 200 /spl mu/m/spl times/1500 /spl mu/m; surface emitters is quite possible, which should allow for the emission of watts of coherent CW power in a stable, single mode. The 2-D structure represents a defect-free, second-order active photonic lattice.

Simultaneous and independent semiconductor laseroperation at 1.3 and 1.55 µm produced by focused ion beam etching

The authors show that, by introducing a single focused ion beam etched cavity into the 1.3 µm bandgap material between the phase tuning and sampled grating sections of a three section DBR laser, sufficient feedback is produced to enable stimulated emission at 1.3, as well as 1.55 µm. The etched cavity also increases the inter-contact resistance.

On the locking range of hybridly mode-locked semiconductor lasers

We theoretically investigate the locking range of hybridly mode-locked semiconductor lasers with a DBR section as a reflector. The DBR coupling constant and length are crucial in determining the locking range. At constant pulse width, the tuning range of the repetition frequency can be increased by a factor of 3 by using a strongly coupled, long DBR rather than a short and weakly coupled DBR. For a 30 GHz cavity and a pulse width of 5 ps, a locking range of 2.5% is predicted after optimization. We explain the increase in the locking range as a consequence of the dispersion inherent to a DBR. In addition, the pulses are found to be asymmetric, depending on the DBR parameters.

Frequency stabilization of tunable DBR laser using multiwavelength light injection locking technique

This paper proposes a frequency stabilization scheme for tunable three-section DBR laser diodes (3S-DBR LD) that use multiwavelength light injection locking. The oscillating wavelength of the SS-DBR LD is discretely switched between cavity modes when the injection current into DBR section is changed, and locked to one wavelength of the multiwavelength light injected from the DBR section facet under the injection locking condition. The light injection properties of the capture range and the relationships of relaxation oscillation versus input power and detuning are investigated experimentally. Injection locking on the multistate wavelength of a tunable DBR LD is performed using a two wavelength multiplexed light. As a result, we demonstrate 1 GHz capture range and more than 26 dB rejection ratio for the multiplexed injected light.

First system experiments with a monolithically integrated tunable polarization diversity heterodyne receiver OEIC on InP

System performance of an integrated polarization diversity heterodyne receiver optoelectronic IC (OEIC) is reported. The OEIC is monolithically integrated on InP. It includes a tunable 4 section DBR laser (quasi continuous tuning range 3.5 nm) and balanced photodiodes. The packaged OEIC is supplied with a fiber pigtail. Stable and polarization independent operation is achieved without any tendency for a bit error floor. The sensitivity at 1550.2 nm is -33.5 dBm at a bitrate of 140 Mbit/s. The performance of the OEIC based receiver is verified by operating in an experimental OFDM-TV distribution system with 4 channels. >

Large optical bistability and self pulsations in three section DBR laser diode

A bistable operation with a hysteresis of 24 mA in the power-current curve of a three section DBR laser is reported. The laser threshold at increasing current is 51 mA while in the opposite direction the laser action is sustained down to 27 mA. The same effect was observed by monitoring the laser threshold through the Bragg and phase section currents. In a large part of the current range which corresponds to the bistable laser operation, strong self pulsations have been observed at frequencies between 1.5 GHz and 3.5 GHz with an amplitude of up to 31.4 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of intensity noise including squeezing in DFB and Fabry-Perot semiconductor laser diodes

A new time-domain model using the quantum formalism of the positive-P distribution is used to investigate squeezing in laser diodes, taking into account longitudinal hole burning and distributed noise sources, under steady-state and large-signal modulation. Simulations indicate that the laser structure determines the lowest achievable intensity noise. With losses present or power escaping from the rear facet, this minimum noise may be much higher than expected from the device quantum efficiency. Squeezing appears more difficult in DFB lasers than in Fabry-Perot lasers in our simulations. Mode-partition noise is removed by low-loss passive DBR sections, and such laser diodes are promising sources with low-intensity noise. Intensity noise in the large-signal dynamic regime is also simulated, showing that intensity-squeezed light output is possible. >

High speed and high density wavelength multichannel butt-jointed DBR lasers

A wavelength multichannel DBR laser exhibiting a −3dB 1M bandwidth up to 8 GHz has been demonstrated. By monitoring only one current in the DBR section, the highest number (18) ever reported of wavelength channels regular spaced has been obtained on a three section DBR structure which was optimised in terms of active-passive coupling efficiency and lengths.

Broadband measurements of frequency noise spectrum in two section DBR laser

The dependence of the frequency noise on the output power, the tuning current and the current modulation has been measured in a two electrode DBR laser from 30MHz to 8GHz. The frequency noise spectrum was fairly flat and decreased with increased output power at a rate faster than l/P. At certain biasing levels, the noise increased and the relaxation peak was shifted towards lower frequencies when current was injected into the passive waveguide. Furthermore, the frequency noise was not affected by the current modulation.

Mode competition and switching in three section DBR tunable lasers

Mode competition in three section DBR tunable lasers is studied with a simple Fabry-Perot like description. The problem is analysed from the point of view of tunable laser applications in multicarrier communication systems. The maximum power for single mode operation and the switching between adjacent modes are discussed.