Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSemiconductor Laser Linewidth Theory Revisited
170
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
More and more applications require semiconductor lasers distinguished not only by large modulation bandwidths or high output powers, but also by small spectral linewidths. The theoretical understanding of the root causes limiting the linewidth is therefore of great practical relevance. In this paper, we derive a general expression for the calculation of the spectral linewidth step by step in a self-contained manner. We build on the linewidth theory developed in the 1980s and 1990s but look from a modern perspective, in the sense that we choose as our starting points the time-dependent coupled-wave equations for the forward and backward propagating fields and an expansion of the fields in terms of the stationary longitudinal modes of the open cavity. As a result, we obtain rather general expressions for the longitudinal excess factor of spontaneous emission ($K$-factor) and the effective $alpha$-factor including the effects of nonlinear gain (gain compression) and refractive index (Kerr effect), gain dispersion and longitudinal spatial hole burning in multi-section cavity structures. The effect of linewidth narrowing due to feedback from an external cavity often described by the so-called chirp reduction factor is also automatically included. We propose a new analytical formula for the dependence of the spontaneous emission on the carrier density avoiding the use of the population inversion factor. The presented theoretical framework is applied to a numerical study of a two-section distributed Bragg reflector laser.
rate research
Read More
We demonstrate a hybrid integrated and widely tunable diode laser with an intrinsic linewidth as narrow as 40 Hz, achieved with a single roundtrip through a low-loss feedback circuit that extends the cavity length to 0.5 meter on a chip. Employing solely dielectrics for single-roundtrip, single-mode resolved feedback filtering enables linewidth narrowing with increasing laser power, without limitations through nonlinear loss. We achieve single-frequency oscillation with up to 23 mW fiber coupled output power, 70-nm wide spectral coverage in the 1.55 $mu$m wavelength range with 3 mW output, and obtain more than 60 dB side mode suppression. Such properties and options for further linewidth narrowing render the approach of high interest for direct integration in photonic circuits serving microwave photonics, coherent communications, sensing and metrology with highest resolution.
Portable mid-infrared (mid-IR) spectroscopy and sensing applications require widely tunable, narrow linewidth, chip-scale, single-mode sources without sacrificing significant output power. However, no such lasers have been demonstrated beyond 3 $mu$m due to the challenge of building tunable, high quality-factor (Q) on-chip cavities. We demonstrate a tunable, single-mode mid-IR laser at 3.4 $mu$m using a high-Q silicon microring cavity with integrated heaters and a multi-mode Interband Cascade Laser (ICL). We show that the multiple longitudinal modes of an ICL collapse into a single frequency via self-injection locking with an output power of 0.4 mW and achieve an oxide-clad high confinement waveguide microresonator with a loaded Q of $2.8times 10^5$. Using integrated microheaters, our laser exhibits a wide tuning range of 54 nm at 3.4 $mu$m with 3 dB output power variation. We further measure an upper-bound effective linewidth of 9.1 MHz from the locked laser using a scanning Fabry-Perot interferometer. Our design of a single-mode laser based on a tunable high-Q microresonator can be expanded to quantum-cascade lasers at higher wavelengths and lead to the development of compact, portable, high-performance mid-IR sensors for spectroscopic and sensing applications.
We derive general analytic expressions for the chromatic dispersion orders valid to infinity, due to the k vector or phase {phi} dependence on the wavelength. Additionally, we identify polynomials and recursion relations associated with the chromatic dispersion orders and draw analogy to the generalized Lah and Laguerre transformations. Further, we give explicitly the dispersion terms to the 10th order and visualize the chromatic dispersion for material, grating and prism-pair compressors and hollow-core photonic anti-resonant fiber. These simple formulas are applicable for material dispersion, compressors, stretchers, waveguides, and any other type of known frequency-dependent phase.
Quantum cascade lasers (QCL) have revolutionized the generation of mid-infrared light. Yet, the ultrafast carrier transport in mid-infrared QCLs has so far constituted a seemingly insurmountable obstacle for the formation of ultrashort light pulses. Here, we demonstrate that careful quantum design of the gain medium and control over the intermode beat synchronization enable transform-limited picosecond pulses from QCL frequency combs. Both an interferometric radio-frequency technique and second-order autocorrelation shed light on the pulse dynamics and confirm that mode-locked operation is achieved from threshold to rollover current. Being electrically pumped and compact, mode-locked QCLs pave the way towards monolithically integrated non-linear photonics in the molecular fingerprint region beyond 6 $mu$m wavelength.
Lasers with high spectral purity can enable a diverse application space, including precision spectroscopy, coherent high-speed communications, physical sensing, and manipulation of quantum systems. Already, meticulous design and construction of bench Fabry-Perot cavities has made possible dramatic achievements in active laser-linewidth reduction, predominantly for optical-atomic clocks. Yet there is increasing demand for miniaturized laser systems operating with high performance in ambient environments. Here, we report a compact and robust photonic-atomic laser comprising a 2.5 cm long, 20,000 finesse, monolithic Fabry-Perot cavity integrated with a micromachined rubidium vapor cell. By leveraging the short-time frequency stability of the cavity and the long-time frequency stability of atoms, we realize an ultranarrow-linewidth laser that enables integration for extended measurements. Specifically, our laser supports a fractional-frequency stability of $1times 10^{-13}$ at an averaging time of 20 ms, $7 times 10^{-13}$ at 300 s, an integrated linewidth of 25 Hz that results from thermal noise, a Lorentzian linewidth as low as 0.06 Hz$^2$/Hz, and a passive vibration immunity as low as $10^{-10}$/g. Our work explores hybrid laser systems with monolithic photonic and atomic packages based on physical design.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
