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

Abstract

Abstract-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 postgrowth 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 ±2 dB over the frequency range 10 MHz to 10 GHz, indicating that tuning times of 100 ps are possible.Index Terms-Integrated optics, ion implantation, laser tuning, quantum-confined Stark effect (QCSE), quantum well intermixing (QWI), tuneable semiconductor lasers.

Phase locking of a 3.4 THz third-order distributed feedback quantum cascade laser using a room-temperature superlattice harmonic mixer

“…Stark electrical tuning however is a very fast process limited only by the RC time constant of the QCL which is typically on the order of pico seconds. 18 To examine this further, we devise a test to observe the bias frequency dependence in the regions both above and below 14.5 V by applying a square wave modulation (DV pp ¼ 4 mV) to the QCL bias voltage. This bias modulation translates into frequency modulation of the QCL emission corresponding to the two bias levels.…”

“…15 The superlattice structure is grown by molecular beam epitaxy on an intrinsic GaAs substrate. It comprises an nþ GaAs layer (thickness 1.5 lm; doping 6Â10 18 cm À3 ), a GaAs/AlAs gradual layer (thickness 32 nm), then the superlattice, again a gradual layer and nþ GaAs and an nþ InGaAs gradual layer (25 nm) and finally an nþ InGaAs layer (20 nm, doping 10 19 cm À3 ) serving as the ohmic contact. The superlattice (length 112 nm) has 18 periods, each period (length 6.22 nm) with 18 monolayers GaAs and 4 monolayers AlAs and was homogeneously doped with silicon (2 Â 10 18 cm À3 ).…”

“…The emission frequency is therefore principally determined by the effective refractive index which, in turn, is determined by (a) its temperature, which causes red shift tuning for increasing bias and (b) the socalled Stark effect in which the energy levels within a quantum well structure are shifted in the presence of an electric field resulting in a change of absorption frequency which, through the Kramers-Kronig relation, induces a corresponding change in refractive index. The Stark effect can result in a red shift or a blue shift, depending on the relative energy alignment of the involved sub-band levels 18,19 and it is FIG. 1.…”

Linear, Low Noise Microwave Photonic Systems using Phase and Frequency Modulation

“…The theoretical modulation efficiency was 2.5 GHz/V, and the spurious intensity modulation was suppessed. More recently, [116] presented a three-section InGaAsP DBR laser. In this device, the passive and active use the same MQW material, but the absorption was reduced in the active sections by using quantum-well intermixing (QWI) based on ion implantation.…”

Photonically enabled agile rf waveform generation by optical comb shifting

“…Here, we present electrical pulses and sinusoids, but more complex shapes are possible with faster photodetectors or higher resolution pulse shapers. This method presents a scalable solution for rapidly switching between many pairs of output waveforms, but it ultimately requires a laser that has been optimized for high-speed frequency modulation [14] to achieve its full potential.…”