Laser_v1 Class Reference

Laser model. More...

Inherits unit.

Public Member Functions
function	Laser_v1 (in param)
	Class constructor. More...
function	traverse (in obj, in varargin)
	Main function call.
function	process (in obj, in varargin)
	save parameters, generate noise More...
function	MaxFreq (in obj)
function	MinFreq (in obj)
function	genNoise (in obj)
	generate noise More...
function	plotLineShape (in obj)
function	plotFMPSD (in obj)
function	plotPNPSD (in obj)
function	plotFreqNoise (in obj)
function	plotPhaseNoise (in obj, in varargin)
function	plot (in obj)
Public Member Functions inherited from unit
function	traverseNode (in obj)
	Set unique ID when creating a unit. More...
function	connectOutput (in obj, in uobj, in unitOutput, in nextUnitInput)
	Specify where signal should go next. More...
function	connectOutputs (in obj, in units, in destInputs)
	Specify where signal should go next. More...
function	writeInputBuffer (in obj, in sig, in inputId)
	write input buffer
function	horzcat (in varargin)
	horizontal concatenation
function	vertcat (in varargin)
	vertical concatenation
function	setparams (in obj, in params, in REQUIRED_PARAMS, in QUIET_PARAMS)
	set parameters More...
function	view (in obj)
	Show interactive GUI through unit_view-class.

Static Public Member Functions
static function	idft (in f, in X, in t)

Public Attributes
Property	nInputs
	Number of inputs.
Property	nOutputs
	Number of outputs.
Property	Fc
	carrier frequency (Hz, can also be set by parameters)
Property	linewidth
	Lorentzian linewidth for standard (non-semiconductor) laser.
Property	Fs
	Sampling frequency (Hz)
Property	Rs
	Symbol rate (/sec)
Property	Lnoise
	Length of the noise signal (samples)
Property	cacheEnabled
	Saves the waveform onto a file for speed porposes.
Property	Power
	Output power (pwr object)
Property	model
	Phase Noise Model (Type PhaseNoiseModel_v1)
Property	limitPn
	Phase noise clipping limit [-1 1]*limitPn.
Property	FMnoiseCal
	Frequency Modulation noise.
Property	PMnoiseCal
	Phase Modulation noise.
Property	fn
	Frequency noise time sequence.
Property	pn
	Phase noise time sequence.
Property	L
	FM noise PSD length.
Property	Lir
	FM noise PSD length.
Property	LFLW1GHZ
	Equivalent linewidth for 1/f noise defined at 1GHz.
Property	HFLW
	High-frequency (Lorentzian-equivalent) linewidth.
Property	fr
	Relaxation resonance frequency.
Property	K
	Damping factor.
Property	alpha
	Linewidth enhancement factor.
Public Attributes inherited from unit
Property	inputBuffer
	Buffer for storing inputs as we traverse the graph.
Property	nextNodes
	Children nodes.
Property	destInputs
	Destination inputs in children.
Property	results
	For storing results.
Property	label
Property	draw
	enable/disable plotting
Property	nInputs
	Number of signals traverse expects.
Property	nOutputs
	Number of outputs traverse expects.

Detailed Description

Laser model.

Outputs a time-domain phase noise sequence with the desired frequency noise power spectral density.

Basic algorithm

1. FM noise PSD is generated in the frequency domain
2. FM noise PSD is converted to time domain using IDFT
3. FM noise PSD is convolved with white Gaussian noise
4. PM noise is generated by integrating FM noise The length of the FM noise PSD is specified in model.Lpsd, or in the constructor, param.L. Noise at the lowest frequency component (DC) is forced to zero unless L=1. This means phase noise will be zero-mean unless L=1.

How to use it

Two ways for using within the Robochameleon framework:

1. Source: Specify signal_interface parameters (Fs,Lnoise)
2. Traverseable: Gets the signal parameters as an input

Two types of operation

1. lorentzian: You need to specifiy linewidth. It creates a flat frequency power spectral density (PSD) at linewidth/pi level, which corresponds to a lorenztian optical spectrum with a FWHM of linewidth.
2. semiconductor: You need to specify LFLW1GHZ, HFLW, fr, K and alpha. It creates the desired semiconductor frequency noise PSD based on those 5 parameters and outputs a time-domain phase noise sequence that matches the desired PSD.

Basic use case: Build a Lorentizan laser with linewidth of 100 KHz at 1550 nm with 2^10 samples

param.laser.Fs = 80e9;
param.laser.Lnoise = 2^10;

Lorentzian examples:

Txparam = struct('Power', pwr(150, {5, 'dBm'}), 'linewidth', 1e5, 'Fc', const.c/1550e-9, 'L', 2^7, ...
     'Fs', param.ppg.Rs*param.ps.US_factor, 'Rs', Rs, 'Lnoise', param.ps.US_factor*L);
LOparam = struct('Power', pwr(150, {5, 'dBm'}), 'linewidth', 1e5, 'Fc', const.c/1550e-9+foffset, 'L', 1);

A laser with Txparam would generate a signal; a laser with LOparam would read many properties from an input signal_interface. The LO uses filter lengths 1, so phase will act like a random walk (no low-frequency noise suppression). The TX uses a long filter, so low-frequency noise will be suppressed. Runtime will also be longer.

SCL example:

SCLparam = struct('Power', pwr(150, {5, 'dBm'}), 'Fc', const.c/1550e-9+foffset, 'L', 2^14, ...
         'alpha', 3, 'fr', 1e9, 'K', .3e-9, 'LFLW1GHZ', 1e6, 'HFLW', 1e5);
badSCLparam = struct('Power', pwr(150, {5, 'dBm'}), 'linewidth', 1e5, 'Fc', const.c/1550e-9+foffset, 'L', 2^14, ...
         'alpha', 3, 'fr', 1e9, 'K', .3e-9, 'LFLW1GHZ', 1e6, 'HFLW', 1e5););

A laser with SCLparam will be a standarad SCL with the properties specified. A laser with badSCLparam will be a Lorentzian, because 'linewidth' will take precedence over alpha, fr, etc. See:

References

M. Iglesias Olmedo, X. Pang, A. Udalcovs, R. Schatz, D. Zibar, G. Jacobsen, S. Popov, and I. T. Monroy, "Impact of Carrier Induced Frequency Noise from the Transmitter Laser on 28 and 56 Gbaud DP-QPSK Metro Links," in Asia Communications and Photonics Conference 2014, OSA Technical Digest (online) (Optical Society of America, 2014), paper ATh1E.1. https://www.osapublishing.org/abstract.cfm?uri=ACPC-2014-ATh1E.1

for definitions of these terms. They are also defined in many other sources (e.g. Coldren & Corzine).

Author

Miguel Iglesias Olmedo

See also

PhaseNoiseModel_v1

Version

1

Definition at line 89 of file Laser_v1.m.

Constructor & Destructor Documentation

function Laser_v1::Laser_v1

(

in

param

)

Class constructor.

Determines whether user wants to take signal parameters from another input signal or to specify them. Also determines whether to operate in Lorentzian or semiconductor laser mode.

Parameters

param.Fs	Sampling frequency [Hz];
param.Rs	Symbol rate [Hz]. Default: nan (Don't use this information).
param.Lnoise	Signal length [Samples].
param.Fc	Carrier frequency [Hz]. Default: 193.41 THz (1550 nm);
param.Power	Output power (pwr object). Default: SNR:inf, P: 0 dBm
param.linewidth	Lorentzian linewidth - forces operation in Lorentzian mode if specified [Hz]
param.LFLW1GHZ	linewidth at 1GHz
param.HFLW	high-frequency linewidth [Hz]
param.fr	relaxation resonance frequency [Hz]
param.K	Damping factor
param.alpha	Linewidth enhancement factor [unitless]

Member Function Documentation

function Laser_v1::genNoise

(

in

obj

)

generate noise

Generates frequency and phase noise time sequences. Generates a time-domain filter with length obj.Lpsd (in constructor, param.L or param.Lir), generates white noise, then filters that noise using the constructed filter. NB: filter will remove DC component of noise if length>1.

Return values

fn	frequency noise sequence
fn	phase noise sequence

function Laser_v1::MaxFreq

(

in

obj

)

This function calls genNoise to generate appropriate phase noise and frequency noise sequences.

function Laser_v1::process	(	in	obj,
		in	varargin
	)

save parameters, generate noise

This function copies signal_interface parameters from input signal if any.

Parameters

varargin

input signal_interface

Return values

fn	frequency noise sequence
fn	phase noise sequence

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The documentation for this class was generated from the following file:

• library/optics/Laser_v1.m