Agilent N4371A
RIN Measurement System
▲ Accurate, high-speed and easy measurements
of RIN frequency characteristics
▲ Reduced uncertainty by using Agilent original
characterization technique (patent pending)
▲ High-speed measurement (5 seconds or less for
20 GHz span, 2000 point, 10 average)
▲ Analysis on multiple traces by various markers
Agilent provides accurate, high-speed
and easy-to-use spectral RIN measurement system by combination of a
sensitive, low-noise optical receiver,
a industry-standard x-series spectrum
analyzer and a digital multi-meter.
RIN (Relative Intensity Noise) is a
parameter representing temporal
intensity fluctuations of a laser signal
and is used as an evaluation index of
the noise characteristic of the laser
devices. RIN is an indispensable item
for indicating the signal quality of both
digital and analog optical transmission
The user interface of N4371A RIN
measurement system shown in figure 2
is easily accessible from the spectrum
analyzer display. The user interface
Figure 1. N4371A RIN Measurement System
N4371A Agilent RIN measurement
system provides accurate RIN measurements with a specially developed
characterization technique (patent
pending) for the photoelectric frequency
response of the entire system. Agilent
RIN measurement system also
reduces uncertainties by removing
the interference by thermal noise
and shot noise precisely.
The measurement speed of N4371A RIN
measurement system is very fast by
special control of the spectrum analyzer.
The measurement time is less than
5 seconds with the condition of a 20 GHz
frequency span, 2,000 frequency points
and 10 times average. The high-speed
measurement enables a real-time
observation of RIN frequency characteristics with varying parameters of
the DUT.
Figure 2. RIN Measurement User Interface
provides functions of displaying up to
5 traces, placing up to 5 markers and
searching minimum or maximum RIN
values in specific frequency range.
System Configuration
Optical Receiver
See Figure 3 Block Diagram
System Software
See Figure 2
X-Series Spectrum Analyzer
See Table 1 (Option: Including PFR, KYB,
MSE, and DVR)
Digital Multi Meter
Agilent 34410A
Optical attenuator
Agilent 81576A or 81577A
Optical multi meter
Agilent 8163B
GP-IB Interface
Agilent 82357B USB/GP-IB interface
Table 1 N4371A Frequency Range and Product Number of MXA-Series Spectrum Analyzer
Frequency Range
100kHz to 3GHz
10MHz to 6.7GHz
10MHz to 13.2GHz
10MHz to 20GHz
MXA Series Option
System Block Diagram
Optical Attenuator
Optical Receiver
USB/GPIB Control
USB Control
Optical Receiver
Multi Meter
PD Temperature Control Circuit
Optical Input
Low Noise
PD Bias Circuit
RF Output
Current Monitor
Figure 3. RIN Measurement System Block Diagram
Measurement Example
In the RIN measurement system, laser
signal from DUT is converted to electric
signal by the PIN-PD in the optical
receiver. The electric signal is amplified by the low noise amplifier and
measured with the Spectrum analyzer.
The average photocurrent of PIN-PD is
monitored by the digital multi meter.
Figure 4 shows a RIN measurement
example of a 1550nm DFB-LD. The RIN
measurement system provides accurate,
fast and easy RIN measurement of a
very low RIN value of -160dB/Hz or
less in a wide frequency range from
10MHz to 20GHz.
The smoothing aperture is selectable
form 0% to 10% in displaying the
measurement results. This function
achieves a high resolution RIN evaluation
with small smoothing aperture, which
enables to capture peaked fluctuation
of RIN characteristics.
The amplified electric signal contains
thermal noise and shot noise as well
as laser intensity noise. The RIN
measurement isolates the amplified
laser intensity noise from other noise
components. The shot noise is calculated from the average photocurrent
and the thermal noise is obtained as
a noise without laser signal. The RIN
measurement system calculate the
laser intensity noise current before
amplification by use of the photoelectric frequency response of the system.
The accuracy of the photoelectric
frequency response significantly
affects measurement results. Agilent
characterizes the response value
precisely by originally developed
methodology. The RIN value is
derived from the laser intensity noise
current and the average photocurrent.
Figure 4. RIN Measurement Example
The measurement results are saved
as table data of the frequency and the
RIN value in CSV file format and as
graphical profiles in PNG file format.
Performance Characteristics
Optionally 81576A/81577A optical
attenuator, 8163B optical multimeter
mainframe and 82357B USB/GP-IB
interface can be included in the system
configuration if the input optical power
control is required for more than 10 dBm
optical source power.
Corresponding Wavelength
1265 nm – 1625 nm
Frequency Range
100 kHz to 3 GHz,
10 MHz to 6.7 GHz/13.2 GHz/20 GHz
Maximum input optical power
≤ +10 dBm @1310 nm and 1550 nm
Minimum RIN
Measurement Value
≤ –160 dB/Hz @0 dBm received optical power;
1310 nm and 1550 nm
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Revised: March 27, 2008
Product specifications and descriptions
in this document subject to change
without notice.
© Agilent Technologies, Inc. 2007, 2008
Printed in USA, May 23, 2008