Relative Intensity Noise Reduction Research Articles

On the Mitigation of RIN Transfer and Transmission Performance Improvement in Bidirectional Distributed Raman Amplifiers

We develop a novel broadband first-order Raman pump for use as a forward pump in transmission experiments. Our results show significant signal relative intensity noise (RIN) reduction, to a level comparable to backward only pumping. The corresponding optical signal to noise ratio can be improved in dual and first-order forward pumped 83.32 km bidirectional distributed Raman amplifiers by using the proposed broadband pump as a first-order pump. A detailed experimental characterization of RIN, signal power evolution and performance of a 10 × 120 Gb/s DP-QPSK coherent wavelength division multiplexing transmission system are presented. We report ∼10 dB RIN reduction and 0.7 dB Q factor improvement, which allows a 1250 km transmission distance increase compared with conventional low RIN and narrowband first-order pump sources. We also demonstrate that, bidirectional pumping with only broadband first-order forward pumping at 50 mW shows the lowest RIN transfer from pump to signal. This extends the transmission reach up to 8332 km with maximum distances increased by 1250 and 1667 km compared with conventional backward only and first-order semiconductor forward pumped bidirectional pumping, respectively.

Optically Injection‐Locked Mid‐IR Quantum‐Cascade Lasers: The Output‐Power–Modulation‐Bandwidth–Noise Trilogy

AbstractA comprehensive study on the output power, the modulation response, and the relative intensity noise (RIN) behavior of an optically injection‐locked mid‐infrared quantum‐cascade laser reveals that the modulation bandwidth and the output power are enhanced in the stable locking range, while the RIN of the slave laser is a superposition of the master and slave noise sources. Since the RIN level of the master laser can even take the lead, a design procedure is introduced to improve the main characteristics of a free‐running laser, including the RIN, the photon lifetime, the modulation bandwidth, and the bias current, using facet reflectivity tailoring. A figure of merit is defined and the RIN reduction of about 20 dB Hz−1 is obtained for very low injection powers compared with the injection‐locked system before the design of master laser.

Relative intensity noise reduction in a dual-state quantum-dot laser by optical feedback.

We report a reduction of the relative intensity noise (RIN) in a dual-state emitting quantum-dot laser subject to the state-selective optical feedback on the ground state and excited state. Numerically, we map the evolution of the RIN for variations of the optical feedback phases for both states. We report important differences in the impact of the feedback when applied to the ground or excited state, and observe regimes for which a significant reduction in RIN is achieved. Experimentally, we confirm these results and achieve a 16dB reduction of the RIN via a careful and independent tuning of the optical feedback phase for each state.

Analytical investigation of relative intensity noise properties of injection-locked mid-IR quantum cascade lasers

In this paper, we develop an analytical approach by linearization of small-signal rate equations in the presence of the Langevin noise sources to investigate the noise properties of mid-IR optically injected locked quantum cascade lasers. Excellent agreement between the reported numerical results and our developed analytical method have been obtained with the advantage of drastic calculation time reduction and deeper system performance knowledge. Then, a comprehensive study has been performed which reveals notable noise reduction, especially near the threshold current. It is shown that increasing the phase difference between the slave and master lasers enhances the corresponding noise term and makes this term the dominant noise-generating process near the locking edges. Additionally, by introducing relative intensity noise (RIN) maps, we demonstrate that increasing the bias current leads to lower RIN and frequency detuning range, while increasing the optical injection power eventuates wider frequency range and also, lower RIN. It has also been discussed that higher linewidth enhancement factors enhance the locking range and decreases the RIN near the positive frequency detuning boundaries. RIN reduction efficiency versus total injected power to the slave laser has been also introduced as a measure of effectiveness of optical injection locking.

Single-Channel 50G and 100G Discrete Multitone Transmission With 25G VCSEL Technology

This paper explores the feasibility of single-channel 50G and 100G transmission using 25G VCSEL technology. We show through experiments the practicality of 50G transmission through 100 m of OM3 multi-mode fiber. To address the question of whether single-channel 100G transmission is feasible, we show through simulation the needed reduction in relative intensity noise of 25G VCSELs and present a novel modulation technique which offers improved performance over conventional discrete multitone with little additional computational complexity.

9.5 dB relative intensity noise reduction in quantum cascade laser by detuned loading

The possibility of reducing the relative intensity noise (RIN) of a quantum cascade laser is demonstrated. By phase-dependent optical feedback from a short, piezo-controlled external cavity configuration, it is possible to achieve up to 9.5 dB of RIN reduction. These findings are consistently explained by a detuned loading approach based on modifying the alpha parameter.

RIN of Mode-Locked External Cavity Lasers Utilizing a Sinusoidally Chirped Fiber Bragg Grating

The relative intensity noise (RIN) of a mode-locked hybrid soliton pulse source (HSPS) utilizing a sinusoidally chirped fiber Bragg grating (FBG) is investigated using the time-domain solution of coupled wave equations and rate equations that include both spontaneous noise and carrier density noise. The effect of some laser diode and grating parameters on the RIN of the HSPS is also described. The numerical results indicate that most parameters affect the system operation even in the absence of noise. RIN reduction at the fundamental frequency is possible in a mode-locked HSPS utilizing a sinusoidally chirped, Gaussian-apodized FBG when compared with an HSPS with linearly chirped gratings. Furthermore, it is also shown that an HSPS utilizing a sinusoidally chirped FBG produces shorter pulses with and without noise than linearly chirped gratings.

Broadband laser enhanced dual-beam interferometry

We demonstrate a dual-beam, balanced detector approach, compatible with commercial Fourier transform infrared spectrometers that provide a single modulated output. Implemented with a near-IR mode-locked fiber laser source and an external broadband polarizing beamsplitter, the dual-beam method provides relative intensity noise reduction and real-time baseline drift cancellation. Noise levels within a factor of three above the shot noise limit (using 0.6 mW of optical power) are demonstrated for the weak second overtone of CO. The method should be particularly well suited for applications like broadband spectroscopy using a large fraction of the supercontinuum generated in a highly nonlinear fiber, and attenuated reflection spectroscopy, for which extreme pathlength enhancement is challenging.

Relative Intensity Noise Reduction by Optimizing Fiber Grating Fabry–Perot Laser Parameters

A set of nonlinear rate equations that can describe an external cavity laser with any arbitrary external optical feedback (OFB) level are derived. A comprehensive study on the relative intensity noise (RIN) characteristics of a fiber grating Fabry-Perot is performed numerically. In this paper, fiber Bragg grating (FBG) is used as a wavelength lasing selective element to control the external OFB level, thereby control the RIN. In addition to the external OFB level, the effect of other external cavity parameters such as temperature, injection current, cavity volume, gain compression factor, and FBG parameters on RIN characteristics is investigated. The temperature dependence (TD) of RIN is calculated according to TD of laser parameters instead of well-known Parkove relationship. Results show that by optimization, the peak value of the RIN can be reduced down to around -150 dB/Hz. The optimum and the shortest external cavity length that provides the minimum RIN is found to be around 3.1 cm. In addition, by optimization, the relaxation oscillation frequency of RIN spectra is shifted toward around 5.6 GHz.

Detailed theoretical investigation on relative intensity noise reduction enhancement based on reflective SOAs

The enhanced performance for relative intensity noise (RIN) reduction based on reflective semiconductor optical amplifiers (R-SOA) has been investigated theoretically by comparison with conventional transmission SOA. The results show that, by selecting appropriate input optical power, as large as >20dB RIN suppression improvement can be achieved for R-SOA, without sacrificing the noise rejection bandwidth. With increased injection current, the optimized input signal power is decreased and the operation region is extended for the best RIN reduction. For RIN suppression in WDM spectrum slicing, the bandwidth optimization of receiver filter should be performed to avoid the spectral broadening induced by self-phase modulation (SPM) and four wave mixing (FWM). Our derived result is helpful for designing and optimizing the R-SOA in application of noise suppression enhancement.

Characterization and Analysis of Relative Intensity Noise in Broadband Optical Sources for Optical Coherence Tomography

Relative intensity noise (RIN) is one of the most significant factors limiting the sensitivity of an optical coherence tomography (OCT) system. The existing and prevalent theory being used for estimating RIN for various light sources in OCT is questionable, and cannot be applied uniformly for different types of sources. The origin of noise in various sources differs significantly, owing to the different physical nature of photon generation. In this study, we characterize and compare RIN of several OCT light sources including superluminescent diodes (SLDs), an erbium-doped fiber amplifier, multiplexed SLDs, and a continuous-wave laser. We also report a method for reduction of RIN by amplifying the SLD light output by using a gain-saturated semiconductor optical amplifier.

Relative-intensity-noise reduction technique for frequency-converted radio-on-fiber system

A radio-on-fiber system is proposed that uses a frequency-multiplexing technique to reduce the relative intensity noise (RIN) caused by reflections at optical fiber connectors. It is based on the simultaneous transmission of IF and local oscillation (LO) frequency. Optimum LO frequency and optical modulation index that minimize RIN are investigated by experiments and calculations assuming the double and multiple reflection situations. The results agree well and RIN reduction of 17 dB is obtained in multiple reflection situations.

Relative intensity noise characteristics of frequency stabilised grating-coupled modelocked semiconductor laser

Relative intensity noise (RIN) characteristics of a frequency stabilised grating-coupled modelocked semiconductor laser (MSL) have been experimentally investigated. Reported is the first measurement, to the authors' knowledge, of general RIN characteristics as well as RIN reduction in the frequency stabilised MSL system showing the relationship between RIN and mode coherency in the MSL.

Mode-locking characteristics and relative intensity noise reduction in hybrid soliton pulse source

The noise and mode-locking phenomena of a hybrid soliton pulse source (HSPS) utilizing different fiber Bragg gratings (FBG) with or without linear chirp are described. The HSPS is modeled by a time-domain solution of the coupled-mode equations including spontaneous emission noise, and relative intensity noise ( RIN ) is calculated using numerical solutions of these equations. It is found that transform-limited pulses over a wide tuning range around the fundamental mode-locking frequency are generated from mode-locked HSPS with linearly chirped uniform and Gaussian apodized FBGs. Mode-locked pulses that are not transform-limited are generated over a wide tuning range from HSPS with Gaussian apodized and uniform FBGs. These gratings can give transform-limited pulses only over a limited tuning range around the fundamental mode-locking frequency. It is also found that RIN reduction is possible for the mode-locked HSPS by selecting a suitable apodization function such as Gaussian and linear chirp rate.

RIN in mode-locked external cavity semiconductor lasers

The relative intensity noise (RIN) of a mode-locked hybrid soliton pulse source (HSPS) utilising a linearly chirped uniform fibre Bragg grating, is investigated, taking into account spontaneous noise, by using coupled-mode equations. It is shown that low noise does not affect the operation of device and therefore transform-limited pulses are generated over a wide tuning range around the fundamental frequency. However, for large values of linewidth enhancement factor, spontaneous coupling factor and gain saturation parameter, transform-limited pulses are not obtained over a wide tuning range because of increasing noise. Hence, the proper mode-locked range reduces. It is also shown that RIN reduction is possible by using linearly chirped uniform gratings as compared to unchirped gratings.

Influence of grating group delay ripple on the reduction of dispersion induced intensity noise in subcarrier multiplexed systems

Linearly chirped fiber Bragg gratings (LCFBGs) have been proposed as a means for reducing dispersion induced intensity noise in subcarrier multiplexed systems. We analyze the effects of group delay ripple in LCFBGs on their ability to reduce dispersion induced intensity noise. We find that for typical ripple periods from 5 to 200 pm, even a 20 ps peak-to-peak amplitude ripple, which is near state-of-the-art performance, can degrade the amount of relative intensity noise reduction provided by LCFBGs.

Reduction of relative intensity noise of the output field of semiconductor lasers due to propagation in dispersive optical fiber

The effect of dispersive, linear propagation (e.g., in single-mode optical fiber) on the intensity noise from semiconductor lasers is investigated. Relations between the frequency and amplitude noise variations of semiconductor lasers are obtained from the laser rate equations and used to calculate the change in the relative intensity noise (RIN) spectrum that occurs during dispersive propagation. Propagation in fiber with positive dispersion (D≳0) over moderate distances (several km for standard single-mode fiber at 1.55 μm) is found to reduce the RIN over a wide range of frequencies. Measurements with a 1.56 μm distributed feedback laser confirm the main theoretical results and demonstrate reductions in RIN of up to 11 dB with 4 km of standard fiber.

New all-optical RIN suppressing, image rejection receiver with efficient use of LO- and signal-power

An all-optical method of achieving a heterodyne signal is presented whereby the local oscillator (LO) relative intensity noise (RIN) and the image channel have been suppressed while efficient use of both LO and signal power is made. This is achieved with only one photodetector, compared to four for the conventional optical-electrical configuration. A 15-dB reduction of LO RIN can be obtained for a relative channel bandwidth of 50%. The image channel of the same bandwidth is suppressed by almost 20 dB.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Relative intensity noise reduction in InGaAs/InP multiple quantum well lasers with low nonlinear damping

The authors demonstrate theoretically and experimentally that the relative intensity noise (RIN) of laser diodes can be dramatically reduced by decreasing nonlinear damping in the laser. Four types of InGaAs/InP multiple quantum well (MQW) lasers with different well widths, barrier widths, and numbers of wells were fabricated. By comparing these four types of devices, it is shown that MQW lasers with wider wells, narrower barriers, and larger numbers of wells have smaller nonlinear damping and lower RIN.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reduction of relative intensity noise in 1.3 μm InGaAsP semiconductor lasers

Relative intensity noise (RIN) from 1.3 μm InGaAsP vapor phase regrown buried heterostructure diode lasers with cavity lengths of 100–300 μm and resonant frequencies exceeding 15 GHz is measured for the first time over the 2.5–18 GHz frequency range. We show that the RIN decreases by nearly 8 dB as the cavity length increases from 100 to 300 μm, and that the RIN is also reduced by lowering the active p-doping concentration. The measured RIN is in excellent agreement with the expression derived from the laser rate equations.