Raman Ring Laser Research Articles

Modelling and characterisation of continuous wave resonantly pumped diamond Raman lasers

We present experimental results and modeling of continuous wave resonantly pumped Raman lasers. The first Stokes diamond Raman ring laser generated 0.6 W at 960 nm with an efficiency of 18%; the second Stokes laser generated 1.5 W at 1485 nm at 9% efficiency. The analytical model, extended to arbitrary Stokes orders, shows the importance of modelling imperfect mode matching and guides the optimization of input and output coupler reflectivity to predict practical watt-level Raman converters of few-watt pump lasers.

Long-haul transmission using counter-pumped distributed Raman ring laser amplification

Long-haul transmission using counter-pumped distributed Raman ring laser amplification

Investigating single-longitudinal-mode operation of a continuous wave second Stokes diamond Raman ring laser.

We report a diamond Raman ring cavity laser resonantly pumped by a tunable Ti:sapphire continuous wave laser. We characterize the laser operation generating first Stokes output and, for the first time, generate second Stokes lasing at a maximum output power of 364 mW with 33.4% slope efficiency at 1101.3 nm. Single longitudinal mode operation is achieved for all first Stokes output powers, but only for lower output powers for second Stokes operation. We discuss possible reasons preventing single longitudinal mode operation.

An Exactly Soluble Equation for the Stationary Probability Distribution in a Nonlinear System under the Influence of Two-telegraph Noise: Application to the Noise Reduction in a Raman Ring Laser

In this paper, we will consider a model of nonlinear system with random telegraph noises and a Raman ring laser by modeling the laser pump light by a pregaussian process and find an exactly soluble equations for the stationary probability distribution of fluctuations in this nonlinear system under the influence of two-telegraph noise. In consequence, we will obtain the so-called noise reduction in this system: the Stokes output of this laser tends to the stabilize under the influence of the broad-band two-telegraph pregaussian pump and compare this results with that obtained in our previous paper (Cao Long Van, Doan Quoc Khoa, Opt. Quant. Electron. 43, 137 (2012)) for the case of one telegraph noise.

Noise reduction in a Raman ring laser by two-telegraph pre-Gaussian pump

We consider Raman ring laser by modeling the laser pump light by a classical time-dependent random process, namely a pre-Gaussian process. It is composed of a finite number of independent so-called telegraphs. The strength of the pre-Gaussian formalism derives from the exact solubility of wide classes of the stochastic equations. In particular we also observed the so-called noise reduction in Raman ring laser: the Stokes output of this laser tends to the stabilize under the influence of the broad-band one-telegraph pre-Gaussian pump (Cao Long and Doan Quoc in Opt Quant Electron 43:137–145, 2012). We extend our model to the case of two-telegraph pre-Gaussian noise and compare obtained results with that obtained in our previous paper for the case of broad-band one-telegraph pre-Gaussian pump.

An exact soluble equation for the steady state probability distribution in a nonlinear system: application to the noise reduction in Raman Ring Laser

In this paper, we consider the model of a nonlinear system subjected simultaneously to a random telegraph noise and a white noise. By using the formulae of differentiation introduced by Shapiro and Loginov (Physica 91:563–574, 1978), an exact equation for the steady state probability distribution of fluctuation in this system is derived. As an example of its application, we calculate analytically the steady state probability distribution of fluctuation and show the existence of noise induced phase transitions (Wodkiewicz et al. in J. Opt. Soc. Am. 1:398–405, 1984a) in Raman Ring Laser. Moreover, we show explicitly the so-called noise reduction considered in Lewenstein and Rzązewski (Opt. Commun. 63:174–178, 1987) for this system. It follows that the Stokes output of this laser tends to the stabilization under influence of the broad-band telegraph pump. This phenomenon could be realized experimentally in a much easer manner than for the case of Gaussian pump, because the construction of the injected telegraph pump signal is much easer than in the case of Gaussian signal. The recent paper is an extended version of Doan and Van (1991).

Small-signal analysis of bidirectional operating characteristics in a Raman ring laser with external optical injections

Employing the small-signal analysis, we study the bidirectional operating characteristics in a Raman ring laser. Bidirectional operation is found not stable in a silicon ring because of the existence of two-photon absorption. Using polar crystals which have different forward and backward Raman gain or introducing external optical injections helps to establish stable bidirectional operation in a Raman ring laser.

Widely tunable Raman ring laser using highly nonlinear fiber

An all-optical widely tunable Raman fiber laser has been realized by incorporating a highly nonlinear fiber in a ring cavity. By feedback a portion of Raman Stokes wave back into the highly nonlinear gain medium, a Raman fiber laser is generated. We found that the lasing wavelength of Raman fiber laser can be tuned from 1537 to 1568 nm with peak power fluctuation within 1 dB, giving a total wavelength tunability of 31 nm. The optical signal-to-noise ratio is found to be wavelength dependent, and the highest optical signal-to-noise ratio of about 59 dB is recorded. The lasing threshold of the Raman fiber laser with this configuration is found to be as low as 300 mW.

Voltage-tuned multiwavelength Raman ring laser with high tunability based on a single fiber Bragg grating

A practical scheme for a tunable multiwavelength Raman fiber ring laser based on a single fiber Bragg grating with a voltage-controllable coil heater is investigated. The number of phase-shifted regions within a single fiber grating determines the number of reflection peaks and the number of lasing wavelengths in the multiwavelength Raman fiber ring laser. A stable multiwavelength Raman fiber ring laser with low output peak-power fluctuation of less than 0.5 dB at room temperature is achieved. A multiwavelength Raman fiber ring laser with a high extinction ratio of more than 50 dB is realized. High flatness is obtained for three lasing peaks, and the lasing peak-power difference is measured to be less than 0.2 dB. A voltage-controllable coil heater with heating elements is used to effectively control three lasing wavelengths in the multiwavelength output, and the tunability of each lasing wavelength is measured to be 0.11 nm/V.

Studies on strain and temperature characteristics of a slanted multimode fiber Bragg grating and its application in multiwavelength fiber Raman ring laser

Detailed strain and temperature characteristics of a 2/spl deg/ slanted multimode fiber Bragg grating (MFBG) are developed theoretically and observed experimentally. Results show that the strain and temperature sensitivities are almost the same for different transmission dips of the 2/spl deg/ slanted MFBG. Utilizing two characteristics of the 2/spl deg/ slanted MFBG, namely 1) resonant wavelength intensities strongly affected by excited mode propagating before the grating and 2) uniform strain sensitivities of different resonant wavelengths, a switchable and tunable multiwavelength fiber Raman ring laser is realized. The configuration is simple and multipurpose. Results show that the laser can generate single-, dual-, three-, four-, and five-wavelength lasing by switching between each operation if a mode scrambler (MS) that is inserted in front of the slanted MFBG is adjusted; furthermore, a 4.2-nm continuous wavelength-tuning range is achieved by straining the slanted MFBG when the MS is fixed.

Inhomogeneous loss mechanism in multiwavelength fiber Raman ring lasers

As one of the mechanisms for stable multiwavelength oscillation in a fiber Raman ring laser, an inhomogeneous loss induced by intraline four-wave mixing in a fiber Raman laser is physically explained and experimentally validated by comparison of laser peak gain and power gain as well as the gain spectra at several pump levels.

Tunable Multiwavelength Fiber Ring Lasers Using a Programmable High-Birefringence Fiber Loop Mirror

We demonstrate a comb filter with digitally tunable wavelength spacing using a programmable high-birefringence (HiBi) fiber loop mirror (FLM). We then use the HiBi-FLM to implement a tunable multiwavelength semiconductor optical amplifier (SOA)-based fiber ring laser and a tunable multiwavelength all-fiber Raman ring laser. Both lasers exhibit stable room-temperature operation and have a wavelength spacing that is digitally tunable between 1.6 and 3.2 nm. With the SOA-based configuration, we obtain six wavelengths with a spacing of 3.2 nm and 11 wavelengths with a spacing of 1.6 nm; with the all-fiber Raman-based configuration, we obtain four wavelengths with a spacing of 3.2 nm and five wavelengths with a spacing of 1.6 nm.

Doppler-induced unidirectional operation of a continuous-wave Raman ring laser in H2.

We demonstrate stable operation of a diode-pumped cw Raman ring laser in diatomic hydrogen gas. Doppler-induced asymmetry between the the forward and the backward Raman gains leads to inherent unidirectional operation in the forward direction without intracavity optical elements. Use of the ring-cavity geometry dilutes the deleterious effects of thermal lensing and significantly reduces optical feedback to the pump laser.

High efficiency, dual-wavelength fibre Raman pump laser for U-band fibre Raman amplifiers

A dual-wavelength, continuous wave, high efficiency fibre Raman ring laser for pumping U-band (1625–1675 nm) fibre Raman amplifiers is demonstrated. Two fibre Bragg gratings were used as wavelength-selective elements resulting in lasing lines at 1529.7 and 1558.7 nm with respective maximum powers of 209.0 and 390.9 mW. A simple U-band Raman amplifier was constructed to test the dual-wavelength pump laser and on:off gain with a peak of 7.3 dB and a 3-dB bandwidth of 73 nm was obtained.

Multi-wavelength, continuous wavefibre Raman ring laser operating at 1.55 µm

A four wavelength, continuous wave, fibre Raman ring laser has been demonstrated at room temperature using fibre Bragg gratings as the wavelength-selective elements with applications as a multi-wavelength source for optical fibre telecommunications. Channel spacings were ~5 nm between 1551.6 and 1565.1 nm with 14.9 dBm total output power.

Improvement of the fiber raman soliton laser for femtosecond optical pulse generation

Abstract Femtosecond optical pulses generated from a synchronously pumped fiber Raman soliton laser (FRASL) have been shown to have large excess noise and high background light (i.e., the pedestal) levels. In this paper, to improve the FRASL, the operation characteristics of the FRASL are investigated both theoretically and experimentally. It is shown that real femtosecond soliton oscillation in the FRASL can be obtained only when the soliton self-frequency shift (SSFS) effect in the fibers is suppressed and proper choices of both the Stokes oscillation wavelength and the pump power level are required for the SSFS suppression in the FRASL. By using a tunable all-fiber Raman ring laser, optical pulses as short as 400 fs with a low white AM noise level of –120 dBc / Hz have been generated from the compact FRASL with SSFS suppression. Based on the theoretical analyses, we propose to use an intracavity saturable absorber to prevent the generation of high-level Stokes background light in the FRASL, and the feasibility of this method is shown by numerical simulations.

Realization of femtosecond soliton oscillation in all-fiber Raman laser with soliton self-frequency shift suppression

In order to obtain the true oscillation of femtosecond solitons in fiber Raman lasers where relatively long fibers are usually used, it is necessary to suppress the soliton self-frequency shift (SSFS) in fibers. The oscillation of femtosecond solitons in a synchronously pumped all-fiber Raman ring laser by suppressing the SSFS effect is described. It is shown that proper choices of both the Stokes oscillation wavelength and pump power level are required for SSFS suppression. Optical pulses as short as 400 fs with low-amplitude noise have been generated from the compact fiber Raman laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tunable CW fibre Raman ring laser centred at 1.41 μm

The first demonstration of a CW tunable fibre Raman ring laser operating around 1.4 μm is reported. This laser was pumped by a 3 W Nd : YAG laser operating at 1.319 μm and tuned over a 10 nm range with a maximum output power of 40 mW.

Noise reduction in a Raman ring laser driven by a chaotic pump: numerical approach

The theory of a single-mode, ring-cavity Raman laser is investigated for a broadband, chaotic pump. The numerical simulations are performed with a realistic model of the noisy pump. A significant reduction of the fluctuations, found in an approximate approach of an earlier paper [ M. Lewenstein K. Rza̧żewski , Opt. Commun.63, 174 ( 1987)], is confirmed. In addition we find a dramatic narrowing of the spectral line.

Intracavity Raman lasers

Experimental and theoretical studies of intracavity Raman lasers are presented. Advantages of intracavity Raman lasers, particularly for low-emission cross section and broadly tunable vibronic gain media, are described. Experimental studies of a hydrogen gas Raman laser pumped inside the cavity of an alexandrite laser are presented. A theoretical model of the dynamics of a unidirectional intracavity Raman ring laser is developed and solved analytically. This model is adapted for simulation experiments.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>