Laser Linewidth

We report on a general theory describing the effect of external optical feedback on the steady-state noise characteristics of single-mode semiconductor lasers. The theory is valid for arbitrarily strong feedback and arbitrary optical feedback configuration and spectrum. A generalized Langevin rate equation is derived. The equation is, in general, infinite order in d / d t constituting an infinite-order correction to the low-frequency weak-feedback analysis. The general formalism includes relaxation oscillations, and allows us to analyze the effect of feedback on both the laser linewidth, frequency noise, relative intensity noise, and the relaxation oscillation sidebands in the field spectrum. The theory is applied to two important feedback configurations; the laser coupled to a single mirror and the laser coupled to a high-Q cavity. The analysis includes excess low-frequency noise due to temperature fluctuations in the laser chip. . His current research interests include spectral and dynamic properties of semiconductor lasers, ultrafast optics, and electrooptic sampling.

The effects of the external optical cavity parameters (external optical cavity length (L-ext), amplitude coupling (C-o) and anti-reflection coating (ARC) reflectivity coefficients) on the noise and modulation spectra of a fiber grating Fabry-Perot laser are numerically analyzed for designing a laser that operates in strong feedback regime (Regime V). Fiber Bragg grating (FBG) is used as a wavelength selective element to control the properties of the laser output by controlling the external optical feedback (OFB) level. The study is performed by modifying a set of rate equations that are solved by considering the effects of external OFB and ambient temperature (T) variations. We proposed a model to calculate the temperature dependence (TD) of laser characteristics according to the TD of laser parameters. An accurate analytical expression for the TD of threshold carrier density (N-th,N- fe) has been derived. The TD of N-th,N- fe was calculated according to the TD of laser cavity parameters instead of using well-known empirical Pankove relationship via the use of characteristics temperature (T-o) and current (I-o). Results show that the optimum external fiber length (L-ext) is 3.1 cm. Also, it is shown that ARC with reflectivity value of 1 x 10(-2) is sufficient for the laser to operate at low noise, good modulation response, and low fabrication complexity.

Link to full text articles :
http://link.springer.com/article/10.1007/s10043-015-0064-y
http://adsabs.harvard.edu/abs/2015OptRv.tmp...44H

In this paper we analyze the impact of the linewidth
over the performance of an optical link in an optical
access network that employs the DPSK modulation
format. We use simulations to measure the BER when
the linewidth of the optical transmitter changes. We
analyze the link performance with different data bit
rates and different dispersion values of the optical
fiber. DPSK is a cheaper and simpler solution compared
with coherent detection. We found that is required
a higher linewidth when the bit rate increases.
This implies a lower cost of implementation of the
access network. In this case, DPSK could be the next
stage to upgrade the intensity modulation format
used in the access networks

We experimentally investigate and theoretically analyze the performance of a multiband orthogonal frequency division multiplexing (MB-OFDM) ultrawideband (UWB) wireless signal over fiber system considering the impact of laser relative intensity noise (RIN). Two types of RIN are considered: laser intrinsic RIN and laser phase-noise-converted RIN due to fiber dispersion. To reduce the impact of intrinsic RIN, laser output power of 2 dBm and beyond should be used. With the increase of fiber length and/or laser linewidth, UWB wireless signal over fiber is more degraded due to the converted RIN. For a given 0.6 dB degradation of error vector magnitude (EVM), the allowed laser linewidth is 30 MHz for 20 km of standard single-mode fiber for the first three bands. However, the converted RIN has much greater impact on higher-frequency UWB channels, depending on fiber length. A laser with a linewidth of less than 1 MHz will ensure that the EVM penalty due to the converted RIN is less than 1 dB for all 14 bands of MB-OFDM UWB.

A report is presented on a general theory describing the effect of external optical feedback on the steady-state noise characteristics of single-mode semiconductor lasers. The theory is valid for arbitrarily strong feedback and arbitrary optical feedback configuration and spectrum. A generalized Langevin rate equation is derived. The equation is, in general, infinite order in d/dt constituting an infinite-order correction to

We revisit the treatment of laser phase noise, with particular application to coherent and differential phase-shift keyed (PSK) systems, developing a considerably simplified yet very accurate analysis based on the phase-noise exponent commutation (PNEC) premise that the receive filtering may be effectively applied in the polar (angular) domain and treating for the first time arbitrary transmit pulses (e.g., return to zero) and optical filter responses (still without intersymbol interference). The PNEC concept directly implies that the angle of the PSK and differential PSK decision statistic is Gaussian distributed, which is verified numerically as very accurate, by means of importance-sampling-based Monte Carlo simulations.

Multi-wavelength laser sources based on Arrayed waveguide grating have been shown in order to provide simultaneously multiples wavelengths with a narrow optical linewidth. Two different laser structures have been developed for the millimeter wave signal generation, monolithically integrated using photonic integrated circuits. In this work we report the characteristics of the heterodyne signal in the millimeter wave range. The optical linewidth measured from the modes generated by different channels on each structure can become less than 150 KHz. Beating the two wavelengths from any of these chips on a high speed photodiode resulted in a beat note having a linewidth less than 250 kHz, which is the narrowest beat-note measured from free running monolithic semiconductor dual wavelength sources.

Coherent optical links enable high-density constellations and, consequently, a higher throughput. However, the phase noise associated with the transmitter and the receiver lasers is a challenging issue in coherent lightwave systems. The authors present an approach that relies on using digital signal processing techniques to compensate for the laser phase-noise effects. The proposed approach exploits the digital processing power to address the problems arising from optical imperfections. The authors present an adaptive filtering scheme that reduces the effect of the laser phase noise and, consequently, relaxes the laser linewidth requirement. The proposed approach shows how the signal processing techniques can be exploited to compensate for the optical impairments by utilizing the continuing scale down in size and power in very large scale integration (VLSI) technology.

This paper deals with the performance evaluation of a passive optical network (PON) using wavelength division multiplexing (WDM) by employing an arrayedwaveguide grating (AWG) in the remote node (RN). In such WDM-based PONs (WDMPONs) the RN demultiplexes the downstream WDM signal via distinct output ports through a static wavelength-routing mechanism. An analytical model is developed for evaluating the bit error rate (BER) performance of the demultiplexed channels as a function of the output port location in the AWG by incorporating a novel spectral-to-spatial domain transformation technique. The proposed model captures the impact of finite laser linewidth as well as the AWG characteristics in determining the received signal power at the individual optical network unit (ONU) attached to the output port (due to spectral-to-spatial mapping). Furthermore, the BER model accounts for several transmission impairments, including beat noise due to interchannel crosstalk in the AWG. Results indicate that the signal power captured by the output ports of AWGs and hence their BER values are not only determined by the Gaussian focal-field pattern of the AWG but also by the power spillover from adjacent ports for broader linewidths and higher data rates. A significant interplay is observed between data rate, source linewidth, and relevant device parameters while examining the loss and BER characteristics of a given AWGbased WDMPON.

En este artículo se analiza el impacto del ancho de línea en el desempeño de una red de acceso óptica en la que se emplea el formato de modulación DPSK. Se demostró, mediante simulaciones, el efecto del ancho de línea sobre la BER (Bit Error Rate). Se analizó el desempeño para diferentes velocidades de transmisión y valores de dispersión en la fibra óptica. DPSK es un formato simple y de menor costo comparado con el uso de detección coherente, DPSK. Se encontró que puede emplearse un mayor ancho de línea al incrementar la tasa de bits, lo que significa un menor costo de implementación. Se propone a DPSK como el siguiente paso en la actualización de la red de acceso actual que emplea modulación en intensidad. Palabras clave: Modulación de fase diferencial, red óptica pasiva, penalidad del ancho de línea.

We develop a simple analytic gaussian model, predicting BER performance of optical DPSK receivers with high accuracy in the wake of all three phase noise sources impairing differential phase detection: linear phase noise (ASE-induced), nonlinear phase noise (the Gordon-Mollenauer effect), and laser phase noise Brownian fluctuations. We validate our analytical Q-factor based formulas using known analytical cases and importance-sampling based Monte-Carlo simulations.

Abstruct-The detection of digital coherent lightwave signals impaired by phase noise is of great current interest. in this paper, we treat waves modulated by either on-off keying (OOK) or binary frequency shift keying (FSK) that are further impaired by additive Gaussian noise. Heterodyne detection of such a waveform produces an electronic handpass signal, which, to ease demodulation in the presence of phase noise, is noncoherently demodulated to extract the baseband pulse stream.

Abstract: We present an Yb:YAG thin-disk oscillator providing a tunable linewidth of 50-pm via VBG-based feedback. Output powers of up to 2 W have been recorded while maintaining an excellent spatial profile. © 2011 Optical Society of America OCIS codes: (140.0140) ...

We demonstrate a straight-forward technique to measure the linewidth of a grating-stabilized diode laser system---known as an external cavity diode laser (ECDL)---by beating the output of two independent ECDLs in a Michelson interferometer, and then taking the Fourier transform of the beat signal. The measured linewidth is the sum of the linewidths of the two laser systems. Assuming that the two are equal, we find that the linewidth of each ECDL measured over a time period of 2 \textmu s is about 0.3 MHz. This narrow linewidth shows the advantage of using such systems for high-resolution spectroscopy and other experiments in atomic physics.

A report is presented on a general theory describing the effect of external optical feedback on the steady-state noise characteristics of single-mode semiconductor lasers. The theory is valid for arbitrarily strong feedback and arbitrary optical feedback configuration and spectrum. A generalized Langevin rate equation is derived. The equation is, in general, infinite order in d/dt constituting an infinite-order correction to

A single frequency Erbium-doped fiber laser (EDFL) operating at 1552.5 nm has been demonstrated by using a 2 m long of newly developed Zirconia-based Erbium-doped fiber (Zr-EDF) as a gain medium. The Zr-EDF is fabricated by combining Zr and Al to achieve the maximum Erbium ion concentration of 4320 ppm wt. By using a fiber Bragg grating (FBG) in a ring configuration, a laser which operates at 1552.5 nm with signal to noise ratio of 60 dB is generated. The linewidth of the EDFL is measured to be approximately 95 MHz using a heterodyne technique.

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