Silicon Raman Laser Research Articles

Pump-to-Stokes relative intensity noise transfer and analytical modeling of mid-infrared silicon Raman lasers

An analytical model for mid-infrared (mid-IR) silicon Raman lasers (SRLs) is developed. The relative intensity noise (RIN) transfer from the pump to the Stokes in the lasers is also investigated. The analytical model can be used as a versatile and efficient tool for analysis, design and optimization of mid-IR SRLs. It is shown that conversion efficiency of 70% is attainable and the low-frequency RIN transfer may be suppressed to below 1 dB by pumping low-loss waveguides at high intensities.

Mid-infrared light generation by high order SRS effect in silicon ring cavity

We have numerically investigated the generation of a fourth order stimulated Raman scattering (SRS) signal in a silicon ring cavity. Output power saturation of the silicon Raman laser has been observed. The influences of effective free carrier life, length of ring cavity and coupling ratio on the signal generation are discussed based on our simulation work. Finally, we put forward a double ring cavity scheme to improve the output characteristics of the silicon Raman laser.

Energy efficient chalcogenide waveguide Raman laser for optical interconnect

We propose and theoretically demonstrate that chalcogenide (As2Se3) waveguide is a more energy efficient platform for Raman amplification and lasing than silicon for optical interconnect applications. In spite of its smaller Raman gain, ultrahigh maximum conversion efficiency of 40%, seven times better than that of silicon Raman laser, is obtained. 33% lasing threshold reduction to 299 mW is simultaneously observed, together with wider linear region. A figure-of-merit (FOM) factor has been established for direct comparison between As2Se3 and silicon waveguide Raman laser. It is found that As2Se3 is superior in terms of energy consumption and device miniaturization capability. Further threshold reduction to 100 mW is achieved by optimizing Stokes end-facet reflectivity.

Recent progress in lasers on silicon

Silicon lasers have long been a goal for semiconductor scientists. This Progress Article reviews the most recent developments in this field, including silicon Raman lasers, the first germanium-on-silicon lasers operating at room temperature, and hybrid silicon microring and microdisk lasers. Challenges and opportunities for the present approaches are also discussed.

Proposal for loss reduction and output enhancement of silicon Raman laser using bi-directional pumping scheme

Based on a novel loss analysis, we numerically demonstrate that bi-directional pumping scheme is an effective technique to achieve loss reduction and maximum output power enhancement in silicon Raman laser. We then investigate the influence of cavity end-facet reflectivity under the bi-directional pumping scheme. Low end-facet reflectivity cavity simultaneously maximizes the output power and enhancement effect of bi-directional pumping, resulting in a fully optimized peak Stokes output.

Terahertz lasing from silicon by infrared Raman scattering on bismuth centers

Stimulated emission at terahertz frequencies (4.5–5.8 THz) has been realized by electronic Raman scattering of infrared radiation on bismuth donor centers in silicon at low temperatures. The Stokes shift of the observed laser emission is 40.53 meV which corresponds to the bismuth intracenter transition between the 1s(A1) ground state and the excited 1s(E) state. The laser has a low optical threshold and the largest frequency coverage in comparison with other Raman silicon lasers based on shallow donor centers. Time-resolved pump spectra enable the separation of donor and Raman lasing.

Raman lasers in silicon photonic wires: unidirectional ring lasing versus Fabry-Perot lasing

Integrated-optical silicon Raman lasers based on a ring cavity can potentially operate unidirectionally owing to the strong non-reciprocity of the Raman gain in submicron photonic wires. This makes the ring-cavity structure significantly more efficient than the alternative Fabry-Perot structure, in which the less efficient of the two propagation directions is unavoidably involved.

Field-atom interaction during four-wave mixing processes in vibronic and Raman lasers

Recently, a new approach to cool optically pumped solid-state lasers by converting the lattice heat into radiation was presented [Laser Phys.18, 430 (2008)]. It relies on a stimulated radiative process occurring in the laser host material. The internal heat gets partially converted through a four-wave mixing process into a radiating optical field. By adopting a Lorentz oscillator model for the field-atom interaction in the laser host, we identified a shortcut to treat the heating and cooling mechanisms going together with the Stokes and anti-Stokes radiation involved in the four-wave mixing. An energy balance between these mechanisms is derived from the differential equation for the material excitation. This balance will ultimately determine the crystal steady-state temperature. This analysis is the first step towards practical engineering implementations of the optical cooling principle for important new laser systems such as the silicon Raman laser and the Cr-ZnSe laser for the mid-IR.

Silicon cascade

After almost 50 years of laser research, efficient and compact laser sources operating in the mid-infrared region from 2 μm to 5 μm are still lacking. Now, cascaded silicon Raman lasers look set to provide a convenient answer.

A cascaded silicon Raman laser

One of the major advantages of Raman lasers is their ability to generate coherent light in wavelength regions that are not easily accessible with other conventional types of lasers1. Recently, efficient Raman lasing in silicon in the near-infrared region has been demonstrated2,3,4, showing great potential for realizing low-cost, compact, room-temperature lasers in the mid-infrared region5,6,7. Such lasers are highly desirable for many applications, ranging from trace-gas sensing, environmental monitoring and biomedical analysis, to industrial process control, and free-space communications8,9. Here we report the first experimental demonstration of cascaded Raman lasing in silicon, opening the path to extending the lasing wavelength from the near- to mid-infrared region. Using a 1,550-nm pump source, we achieve stable, continuous-wave, second-order cascaded lasing at 1,848 nm with an output power exceeding 5 mW. The laser operates in single mode, and the laser linewidth is measured to be <2.5 MHz.

Cooling Silicon Raman Lasers with Coherent Anti-Stokes Raman Scattering

Cooling Silicon Raman Lasers with Coherent Anti-Stokes Raman Scattering

Application of defect engineering to silicon Raman lasers and amplifiers

Silicon Raman lasers and amplifiers are the only silicon-based, monolithic device structures in which optical gain has been unambiguously observed. The main limitation on this gain is optical absorption due to free carriers, generated by two photon absorption. Here we explore a means to mitigate carrier effects via defect engineering. The optical and electrical properties of the defected silicon waveguides are modeled for both a uniform defect distribution and a remote, localized defect distribution. Simulation results indicate that a uniform defect distribution provides no improvement with any increase in net gain provided solely by surface modification. In contrast, for devices with remote defect volumes the reduction of carrier lifetime and limited optical absorption results in a significant improvement to net gain.

Mitigating Heat Dissipation in Raman Lasers Using Coherent Anti-Stokes Raman Scattering

We present a novel technique that intrinsically mitigates the quantum-defect heating in Raman lasers. The basic principle of this so-called "coherent anti-Stokes Raman scattering (CARS)-based heat mitigation" is to suppress the phonon creation in the Raman medium by increasing the number of out-coupled anti-Stokes photons with respect to the number of out-coupled Stokes photons. We demonstrate with the aid of numerical simulations that for a hydrogen and a silicon Raman laser, CARS-based heat mitigation efficiencies of at least 30% and 35%, respectively, can be obtained.

Intracenter Raman silicon lasers

Raman-type Stokes stimulated emission in the far-infrared wavelength range (52–65 μm) has been realized in silicon crystals doped by group-V hydrogen-like donor centers at low temperatures under optical excitation by radiation from a pulsed frequency-tunable infrared free-electron laser. The light scattering appears as an entire intracenter process and occurs on the donor electronic transitions being resonant to the intervalley transverse acoustic g phonon. The outgoing and incoming electronic donor resonances amplify the efficiency of scattering, so that the Raman optical gain increases to the values observed for the infrared room temperature Raman silicon lasers.

Low-threshold continuous-wave Raman silicon laser

We report the first demonstration of a low-threshold continuous-wave (c.w.) Raman silicon laser based on a ring-resonator-cavity configuration. We achieved a lasing threshold of 20 mW, slope efficiency of 28% and an output power of 50 mW, with a 25 V reverse bias applied to the p-i-n silicon waveguides. This represents nearly a tenfold improvement in the lasing threshold and more than a fivefold improvement in both slope efficiency and output power over previous results. In addition, we demonstrate for the first time c.w. lasing with zero bias voltage. In this arrangement, the laser does not require an external electrical power supply, and we obtained a lasing threshold of 26 mW and laser output power exceeding 10 mW. The realization of low-threshold lasing and lasing with no external bias is a major advance towards producing practical silicon lasers based on stimulated Raman scattering, for applications ranging from telecommunications and interconnects to optical sensing and biomedical applications.

Prospects for Silicon Mid-IR Raman Lasers

This paper presents the case for the silicon Raman laser as a potential source for the technologically important midwave infrared (MWIR) region of the optical spectrum. The mid-IR application space is summarized, and the current practice based on the optical parametric oscillators and solid state Raman lasers is discussed. Relevant properties of silicon are compared with popular Raman crystals, and linear and nonlinear transmission measurements of silicon in the mid-IR are presented. It is shown that the absence of the nonlinear losses, which severely limit the performance of the recently demonstrated silicon lasers in the near IR, combined with unsurpassed crystal quality, high thermal conductivity and excellent optical damage threshold render silicon a very attractive Raman medium, even when compared to the very best Raman crystals. In addition, silicon photonic technology, offering integrated low-loss waveguides and microcavities, offers additional advantages over today's bulk crystal Raman laser technology. Using photonic crystal structures or microring resonators, the integrated cascaded microcavities can be employed to realize higher order Stokes emission, and hence to extend the wavelength coverage of the existing pump lasers. Exploiting these facts, the proposed technology can extend the utility of silicon photonics beyond data communication and into equally important applications in biochemical sensing and laser medicine

Cascaded silicon Raman lasers as mid-infrared sources

It is shown by numerical simulations that cascaded silicon Raman lasers, in which the pump light undergoes multiple Stokes shifts in a silicon waveguide, can efficiently convert near-IR to mid-IR radiation. For pump wavelengths significantly below 2 µm, two-photon-absorption-induced free-carrier absorption degrades conversion efficiency, and the effective carrier lifetime determines the shortest possible pump wavelength.

Energy harvesting in silicon Raman amplifiers

Continuous-wave Raman amplification in silicon waveguides with negative electrical power dissipation is reported. It is shown that a p-n junction can simultaneously achieve carrier sweep-out leading to net continuous-wave gain and electrical power generation. The approach is also applicable to silicon Raman lasers and other third-order nonlinear optical devices.

Strained silicon as a new electro-optic material

For decades, silicon has been the material of choice for mass fabrication of electronics. This is in contrast to photonics, where passive optical components in silicon have only recently been realized. The slow progress within silicon optoelectronics, where electronic and optical functionalities can be integrated into monolithic components based on the versatile silicon platform, is due to the limited active optical properties of silicon. Recently, however, a continuous-wave Raman silicon laser was demonstrated; if an effective modulator could also be realized in silicon, data processing and transmission could potentially be performed by all-silicon electronic and optical components. Here we have discovered that a significant linear electro-optic effect is induced in silicon by breaking the crystal symmetry. The symmetry is broken by depositing a straining layer on top of a silicon waveguide, and the induced nonlinear coefficient, chi(2) approximately 15 pm V(-1), makes it possible to realize a silicon electro-optic modulator. The strain-induced linear electro-optic effect may be used to remove a bottleneck in modern computers by replacing the electronic bus with a much faster optical alternative.

Nonlinear absorption in silicon and the prospects of mid‐infrared silicon Raman lasers

AbstractWe present the first experimental results of nonlinear absorption in silicon at the mid infrared wavelengths. Nonlinear losses due to two‐photon and free‐carrier absorption that are found to degrade near infrared silicon Raman devices become negligible at photon energies less than half the bandgap (i.e., λ &gt; 2.2 µm in wavelength). Moreover, the low loss window for linear absorption in silicon extends from 1.2 to 6.5 µm. These factors along with the excellent thermal conductivity and high optical damage threshold renders silicon an ideal material for building Raman lasers and amplifiers that operate in the mid infrared wavelengths. This new technology will expand the application space of silicon photonics beyond data communication and into biochemical sensing, laser medicine, and LIDAR. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)