1.55 µm AlGaInAs/InP sampled grating laser diodes for mode-locking at THz frequencies

We report mode locking in lasers integrated with semiconductor optical amplifiers, using either conventional or phase shifted sampled grating distributed Bragg reflectors(DBRs). For a conventional sampled grating with a continuous grating coupling coefficient of ~80 cm-1, mode-locking was observed at a fundamental frequency of 628 GHz and second harmonic of 1.20 THz. The peak output power was up to 142 mW. In the phase shifted sampled grating design, the grating is present along the entire length of the reflector with π-phase shift steps within each sampled section. The effective coupling coefficient is therefore increased substantially. Although the continuous grating coupling coefficient for the phase shifted gratings was reduced to ~23 cm-1 because of a different fabrication technology, the lasers demonstrated mode locking at fundamental repetition frequencies of 620 GHz and 1 THz, with a much lower level of amplified spontaneous emission seen in the output spectra than from conventional sampled grating devices. Although high pulse reproducibility and controllability over a wide operation range was seen for both types of grating, the π-phase-shifted gratings already demonstrate fundamental mode-locking to 1 THz. The integrated semiconductor optical amplifier makes sampled grating DBR lasers ideal pump sources for generating THz signals through photomixing

THz Repetition Frequency Mode-Locked Laser Using Novel Sampled Gratings

Conventional sampled grating distributed-Bragg-gratings (C-SGDBRs) are widely used in tunable DBR lasers [1], and more recently have been used to precisely control the wavelength spacing in arrays of DBR lasers for use in WDM systems [2], and as the reflectors in THz repetition frequency (Fr) semiconductor mode locked lasers (SMLLs) [3]. However, the effective coupling coefficient, κ, of a C-SGDBR (Fig. 1(a)) is necessarily reduced substantially from that of a uniform grating because much of the sampled grating period has no grating. Here, for the first time, we apply a combination of π-phase shifted gratings, previously demonstrated in fiber lasers [4], with the C-SGDBR technique to THz repetition frequency SMLLs. Using a single electron beam lithography (EBL) step we have demonstrated a 620 GHz side-wall SGDBR MLL with an increased effective κ

Integrated Phase-locked Laser Diodes at 1.55μm

Two types of integrated phased locked laser diodes operating at 1.55 μm were demonstrated, using either a distributed feedback laser seeding source or a self-locking multi-mode interference array. Both exhibited far field patterns that reflected mutual coherence between the light from the output waveguides

Declining Exhaustible Resource Rent with Small, Distinct Extractive Firms

We consider a competitive extraction industry comprising many small firms, each with a slightly different quality of mineral holdings. With "rapidly" declining quality of holding per firm we observe rent declining over and interval. We do not work with the planning solution, commonly invoked in the study of firms with distinct qualities of stock.exhaustible resources, resource rent, competitive extraction

The Extractive Firm's Cost Spillover Tax for the Extended Hotelling Model

We consider a competitive extraction industry comprising many small firms, each with a slightly different quality of mineral holdings. With "rapidly" declining quality of holding per firm, we observe rent declining over an interval. We then take up the familiar planning model and isolate the tax required to make decentralized extraction by many distinct, competitive firms replicate the planning solution.exhaustible resources, resource rent, competitive extraction, corrective tax

The economics of Communist Party membership - The Curious case of rising numbers and wage premium during China’s transition

Why is it that, as the Chinese Communist Party has loosened its grip, abandoned its core beliefs, and marketized the economy, its membership has risen markedly along with the economic benefits of joining? We use three national household surveys, spanning eleven years, to answer this question with respect to labour market rewards in urban China. We conceptualize individual demand for Party membership as an investment in “political capital” that brings monetary rewards in terms of higher wages. This wage premium has risen with the growing wage differentials associated with the emergence of a labour market and the continuing value of political status in the semi-marketized transitional economy. However, a demand-side explanation does not explain the fact that the wage premium is higher for the personal characteristics that reduce the probability of membership. We develop an explanation in terms of a rationing of places and a scarcity value for members with those characteristics.China, Communist Party, labour market, economic transition, wages

Extracting bull and bear markets from stock returns

Traditional methods used to partition the market index into bull and bear regimes often sort returns ex post based on a deterministic rule. We model the entire return distribution; two states govern the bull regime and two govern the bear regime, allowing for rich and heterogeneous intra-regime dynamics. Our model can capture bear market rallies and bull market corrections. A Bayesian estimation approach accounts for parameter and regime uncertainty and provides probability statements regarding future regimes and returns. Applied to 123 years of data our model provides superior identification of trends in stock prices.Markov switching, bear market rallies, bull market corrections, Gibbs sampling