THORLABS SA201 User manual

SA201, SA201-EC
Spectrum Analyzer Controller
Operating Manual

Spectrum Analyzer Controller
Page 1 Rev D, February 26, 2013
Table of Contents
Chapter 1 Overview............................................................................ 3
1.1.1. Parts List......................................................................................3
1.1.2. Compatible Fabry-Perot Scanning Heads ...................................3
Chapter 2 Description........................................................................ 5
Chapter 3 Operation.........................................................................10
3.1. PD Blanking Circuit ...................................................... 10
3.2. Replacing the Fuse....................................................... 11
1.1.3. Cleaning.....................................................................................12
Chapter 4 Recommended Setup..................................................... 13
Chapter 5 Specifications .................................................................14
Chapter 2 Regulatory....................................................................... 17
Chapter 3 Thorlabs Worldwide Contacts....................................... 18

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Table of Figures
Figure 1: SA201 Front Panel Controls ............................................................... 5
Figure 2: Trigger Logic....................................................................................... 7
Figure 3: Saw tooth Waveform (left), Triangle Waveform (right)........................ 7
Figure 4: SA201 Rear Panel Connections ......................................................... 8
Figure 5: Recommended Setup Diagram ........................................................ 13

Spectrum Analyzer Controller
Page 3 Rev D, February 26, 2013
Chapter 1 Overview
The SA201 is specifically designed to control Thorlabs SA200 Series Fabry Perot
Interferometers. The controller generates a voltage ramp, which is used to scan
the separation between the two cavity mirrors. The controller provides
adjustment of the ramp voltage and scan time, allowing the user to choose the
scan range and speed. An offset control is provided to allow the spectrum
displayed on the oscilloscope to be shifted right or left. Another convenient
feature of the controller is a zoom capability that provides a 1X, 2X, 5X, 10X,
20X, 50X and 100X increase in the spectral display resolution. The output TTL
level trigger allows the user to externally trigger an oscilloscope on either the
beginning or midpoint of the ramp waveform.
The SA201 also includes a high precision photodetector amplifier circuit used to
monitor the transmission of the cavity. The amplifier provides an adjustable
transimpedance gain of 10K, 100K, and 1M V/A when driving a high impedance
load, such as an oscilloscope. Using the output sync signal from the controller,
an oscilloscope can be used to display the spectrum of the input laser. The
detector circuitry incorporates a blanking circuit, which disables the photodiode
response during the falling edge of the saw tooth waveform.
1.1.1. Parts List
Below is a list of all components shipped with the SA201 Spectrum Analyzer
Controller.
•SA201 Spectrum Analyzer Controller
•Operating Manual
•120 VAC US Power Supply Line Cord (with the SA201) or 230 VAC
Power Supply Line Cord for Europe (with the SA201-EC)
•125 mA Fuse for use at 230 VAC operation (250 mA fuse installed in
unit)
1.1.2. Compatible Fabry-Perot Scanning Heads
This product has been designed to be used with one of our SA200 or SA210
Series Scanning Fabry-Perot Interferometers. Below is a list of available heads.
Note this list is subject to change without notice. Please visit the website for the
most current information.

SA201, SA201-EC Chapter 1: Overview
6679-D02 Page 4
Item # Description
SA200-3B 350-535 nm, 1.5 GHz FSR
SA200-5B 535-820 nm, 1.5 GHz FSR
SA200-7A 780 - 930 nm, 1.5 GHz FSR
SA200-8B 820-1275 nm, 1.5 GHz FSR
SA200-9A 900 - 1100 nm, 1.5 GHz
FSR
SA200-12B 1275-2000 nm, 1.5 GHz
FSR
SA200-14A 1450 - 1625 nm, 1.5 GHz
FSR
SA200-18B 1800-2500 nm, 1.5 GHz
FSR
Item# Description
SA210-3B 350-535 nm, 10 GHz FSR
SA210-5A 525-650 nm, 10 GHz FSR
SA210-5B 535-820 nm, 10 GHz FSR
SA210-7A 780-930 nm, 10 GHz FSR
SA210-8B 820-1275 nm, 10 GHz FSR
SA210-9A 900-1100 nm, 10 GHz FSR
SA210-12A 1250-1400 nm, 10 GHz FSR
SA210-12B 1275-2000 nm, 10 GHz FSR
SA210-14A 1450-1625 nm, 10 GHz FSR
SA210-18B 1800-2500 nm, 10 GHz FSR

Spectrum Analyzer Controller
Page 5 Rev D, February 26, 2013
Chapter 2 Description
Figure 1 SA201 Front Panel Controls
Detector Gain Adjustment
The SA201 includes a built in photodiode amplifier circuit. This amplifier is
designed specifically to operate with the detector provided with the SA200 series
Fabry Perot Interferometer, allowing the user to monitor the transmission of the
cavity. While any photodetector may be connected to the amplifier the
specifications, listed in Section 1, apply only to detectors supplied with the SA200
series. The amplifier provides a transimpedance gain (current to voltage gain) of
10K, 100K, and 1M V/A while driving a Hi-Z load, such as an oscilloscope. For
better noise and performance characteristics it is recommended that a 50 W coax
cable with a 50 Ωterminating resistor be used. The Photodetector input and
output BNC’s are located on the rear panel.
DC Offset Control
The DC Offset provides a continuously adjustable offset voltage over the range
of 0 to 15 V using a 10-turn potentiometer. This offset adds directly to the ramp
signal. The DC offset control is used to adjust the waveform from left to right
across an oscilloscope viewing window, without affecting the calibration of the
cavity.
Detector Gain
DC Offset Control
Sweep Expansion
Waveform Control
Power Switch
Power On Indicator
Amplitude Control
Rise Time Trigger Output BNC
Output

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6679-D02 Page 6
Sweep Expansion Control
The sweep expansion provides a zoom capability to increase the spectral display
resolution by a factor of 1x, 2x, 5x, 10x, 20x, 50x, and 100x. This is achieved by
scaling the ramp rise time to the sweep expansion.
Waveform Control
The SA201 allows the user to select between a saw-tooth and triangular
waveform. The saw-tooth waveform is desirable for most applications; however
the triangle waveform is useful for cavity alignment. The SA201 will default to the
saw-tooth waveform during the system power-up. To change the waveform,
simply press the ‘WAVEFORM SEL’ button. The selected waveform is indicated
by the illuminated symbol to the right of the waveform select button.
Power Switch
The power switch is used to toggle the unit on and off.
Power On Indicator
The power on LED will light when the unit is powered up.
Amplitude Control
The amplitude control allows the user to adjust the ramp amplitude from 1 to 30
V peak to peak using a 10-turn trim pot. Note, the ramp signal is added to the DC
offset. This means that when the offset is set to 0V, the ramp will start a 0V and
increase to the amplitude limit setting. The amplitude is used to determine how
far the mirror will be scanned, or to set the spectral range of the optical head.
Rise Time Control
The rise time control allows the user to continuously adjust the scan rate from
0.01 to 0.1 ms using a 10-turn trim pot. Note the rise time setting may be scaled
by the sweep expansion setting. For example: If the scan rate is set to 0.05 s and
the sweep expansion is adjusted from 1x to 100x then the scan rate will adjust to
5 s. The scaling error is typically less than ±0.5%, providing excellent
measurement capabilities.
Trigger Output BNC
This trigger output signal may be used to externally trigger the oscilloscope. The
trigger is capable of driving 50 Ωterminated cables, as well as Hi Z loads such
as oscilloscopes. The trigger will provide an edge on the beginning and middle of
the scanning ramp. See Figure 2 below.

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Page 7 Rev D, February 26, 2013
Figure 2 Trigger Logic
Output BNC
The output BNC is used to drive the SA200 scanning piezos from 1 to 45 V. The
output is capable of driving 0.6 µF piezo loads at a ramp rate of 1 ms over the full
voltage range. The output current is internally limited to prevent damage to the
output drive. Note: the output performance specifications assume a Thorlabs
Fabry Perot Interferometer module is connected.
Figure 3 Saw tooth Waveform (left), Triangle Waveform (right)

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Figure 4 SA201 Rear Panel Connections
Ground Plug
This ground plug is for use as a general-purpose ground connection. It is
connected directly to the earth ground connection of the input power plug.
AC Input Connector
This is the line voltage input connection. IMPORTANT: The unit is configured for
100/115 VAC, 50 – 60 Hz from the factory. To operate at 230 VAC see page 11.
PD Amplifier Input BNC
This input BNC is used to interface the photodetector, provided with the SA200
scanning heads, to the amplifier circuit. The photodiode amplifier is configured to
operate with the Thorlabs supplied photo detectors; however it is possible to
operate user supplied photo detectors. To do so, the BNC center contact must be
connected to the photo detector cathode and the BNC shell must be connected
to the photodiode anode (unbiased operation). If a biased detector is to be used
the BNC shell must be connected to the bias ground and the bias voltage must
be negative for the circuit to operate properly.
PD Amplifier Output BNC
This BNC is the amplifier output and may be connected directly to an
oscilloscope to view the cavity spectrum. The amplifier gain will be set using the
front panel ‘DETECTOR’ control knob. The amplifier output includes a 50 Ω
series resistor to minimize noise when operating with a 50 Ωcoax cable. For best
Ground Plug
A
C Input Connecto
r
PD Amplifier Input BNC
PD Amplifier Output BNC
Voltage Selector

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Page 9 Rev D, February 26, 2013
results, a 50 Ωload resistor is recommended at the oscilloscope. Note, the
amplifier gain will be halved with a 50 Ωload connected.
Voltage Selector Switch
The voltage selector switch allows the user to select the input line voltage. The
factory default setting is 100/115 VAC as shown in figure 4. To operate at 230
VAC, this switch will have to be moved to the 230 V position. The line fuse will
also need to be changed to properly protect the unit. See page 11 for detailed
instructions.