Newport 2051 User manual

U S E R ’ S G U I D E
10-MHz Adjustable
Photoreceivers
Models 2051 & 2053
These photoreceivers are sensitive to electrostatic
discharges and could be permanently damaged if
subjected even to small discharges. Ground your-
self adequately prior to handling these detectors
or making connections. A ground strap provides
the most effective grounding and minimizes the
likelihood of electrostatic damage
phone: [phone]
e-mail: [e-mail] • www.newport.com

Warranty
Newport Corporation guarantees its products to be free of defects for one
year from the date of shipment. This is in lieu of all other guarantees,
expressed or implied, and does not cover incidental or consequential loss.
Information in this document is subject to change without notice.
Copyright 2022, Newport Corporation. Allrights reserved.
The New Focus logo and symbol are registered trademarks of Newport
Corporation
Document Number 90099908 Rev. A

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Models 2051 & 2053
Contents
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Using the Photoreceiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Checking the Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9selpicnirP&serutaeFlareneG
Photoreceiver Circuitry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Optical Power and Output Voltage . . . . . . . . . . . . . . . . . . . . . 11
Frequency Response and Noise 13
Measuring Bandwidth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Measuring Noise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Performance Data for Frequency Response. . . . . . . . . . . . . .16
Performance Data for Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
21scitsiretcarahC
Physical Speci cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Model 2051 Spec cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Model 2053 Spec cations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
24ecivreSremotsuC
Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

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Operation
Introduction
The Model 205X is a general-purpose photoreceiver
with adjustable gain and bandwidth. These receivers
can be powered by batteries or by an external ± 15-V
power supply. There are two models available, each
based on a di erent photodetector. Free-space (FS) and
ber-coupled (FC) versions are available for each
model:
Complete speci cations begin on page 21.
The 10-MHz three-stage transimpedance ampli
includes selectable gain and selectable low- and high-
pass lters for easy signal optimization.
Model Wavelength Diode
Type Active Area
2051-FC 300–1070 nm silicon 0.8 mm2
2051-FS 300–1070 nm silicon 0.8 mm2
2053-FC 900–1700 nm InGaAs 0.0078 mm2
2053-FS 900–1700 nm InGaAs 0.08 mm2
Note:
Note:

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Figure 1:
Typical
responsivities
of the Model
2051 & 2053
photodiodes
To obtain the value of the “response factor” in V/mW, divide the
photodiode responsivity by 1.5. For more information on
frequency response and noise, see page 13.
800
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)
400
Responsivity (A/W)
1200 1600
2051
2053
Note:
Note:

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Using the Photoreiver
1. Mount the photoreceiver.Use the 8-32 thread (M4 for
metric versions) on the bottom of the casing to mount
the photoreceiver to a post or pedestal.
2. Supply power. Power the Model 205X using either two
9-volt alkaline batteries or a ± 15-V low-noise linear
power supply (such as the Newport Model 0901).
3. Connect the receiver output. Connect your voltmeter,
oscilloscope, or other instrument to the Output SMA
connector on the receiver.
If you wish to connect to a BNC cable, you can purchase a
BNC-to-SMA adapter such as the Newport Model 1225.
4. Turn on the photoreceiver power. For external power,
use±15 VDC ON; for battery, use Batt Mode ON.
5. Align the optical beam onto the detector. The
photodiode is not very large, so take care when aligning
the beam.
6. Adjust the gain.Use the knob and rocker switch on the
receiver to set the gain. The bandwidths vary with the
gain setting (see table on page 10).
7. Adjust the filters. Select low-pass and high-pass corner
frequencies using the knobs on the receiver.
8. Turn off the photoreceiver power. When you are
finished with the receiver, place the power switch in the
±15 VDC ONposition and switch off or unplug the
external power supply.
Checking the Batteries
The Model 205X can be powered by two standard
9-volt alkaline batteries. Under normal operating
Note:
Note:

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conditions with low light levels and a high impedance
load attached to the BNC connector, the photoreceiver
draws about 20 mA from the batteries, and the battery
lifetime is approximately 24 hours.
To check the condition of the battery:
1. Turn on the photoreceiver using the power switch.
2. Set theLow Frequency adjustment to DC.
3. Set theGain to 3x104.
4. Focus at least 1 µW of optical power on the
detector (or place the detector in front of a desk
lamp).
The output should be greater than 7 V. If it is not,
replace the batteries with fresh ones.
Replacing the Batteries
The Model 205X is shipped with two fresh 9-V
batteries installed. To avoid confusion due to low
batteries, replace the batteries on a monthly basis
when the receiver is in frequent use, or use an external
linear power supply such as the Newport Model 0901.
1. Turn o the receiver using the power switch.
2. Use a Phillips-head screwdriver to remove the
two screws on the back panel of the photo-
receiver.
3. Remove the back panel.
4. Replace the used 9-V batteries with fresh ones.
5. Replace the back panel and the two screws.
6. Recheck the battery level as described above.

Models 2051 & 2053 General Features & Principles •9
General Features & Principles
Photoreceiver Circuitry
The circuitry inside the Model 205X consists of a
photodiode followed by a three-stage transimpedance
amplier. The gain can be adjusted from 626 V/A to
18.8x106V/A in 5-dB steps. The low-noise amplier
design is optimized to maximize bandwidth at each
gain setting. At the higher gain settings, the bandwidth
is limited by amplier gain-bandwidth product. The
plots of Figure 3 show the typical frequency responses
for the dierent gain settings.
Figure 2:
Functional
schematic of
the Model 205X
circuitry
+15 V
-15 V
GND
BATT
9 V
INDEPENDENTLY
ADJUSTABLE 6-dB/OCTAVE
HIGH- AND LOW-PASS FILTERS
+9 V
DETECTOR
HOUSING IS
GROUNDED
SMA
ADJUSTABLE-GAIN
STAGE
x3
x1
ADJUSTABLE-GAIN
STAGE
x104
x103
x102
x10
x1
f_L f_H
BATT
9 V
+9 V REG
-9 V REG
+9 V
-9 V

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The following table summarizes the bandwidth at each
gain setting. The bandwidth on the 3x settings is
somewhat lower than the 1x settings, and signicantly
decreases at the highest gain settings. There is little
dierence in frequency response between the visible
(Model 2051) and IR (Model 2053) models. The plots of
Figure 3 show the frequency-response details for each
gain setting.
Optical Power and Output Voltage
The typical operating range for these receivers is from
a few nanowatts up to 2 to 5 mW (depending on the
model and gain setting). Be careful to keep the optical
power below the maximum optical power of 10 mW
to avoid damaging the photoreceiver.
To compute the approximate output voltage for a given
input optical power use the relationship
Vout= P·R·G,
Gain
SettingSpecication Typical Performance
1x1 10 MHz 12 MHz
3x1 NA 6 MHz
1x10 NA 12 MHz
3x10 NA 6 MHz
1x102NA 8 MHz
3x102NA 6 MHz
1x103NA 700 kHz
3x103NA 700 kHz
1x104NA 250 kHz
3x104150 kHz 250 kHz

Models 2051 & 2053General Features & Principles •11
wherePis the input optical power in Watts,Ris the
photodetector’s response factor in V/mW, and Gis the
amplier’s gain setting.
Estimate the value of the response factor by dividing the
responsivity shown in Figure 1 by 1.5.
For example, the Model 2051 on the 1x103gain setting
and with 10 µW of optical power at 900nm on the
photodiode will have an output voltage of
approximately
(0.01 mW)·(0.35 V/mW)·(1x103) = 3.5 V.
The maximum dierential optical power that can be
detected by the photoreceiver is determined by the
input optical power at which either stage of the
transimpedance gain saturates. We can calculate the
saturation power at 900 nm for the Model 2051 at its
maximum output voltage of ±7 V with fresh batteries
or operating from an external ±15 VDC power supply.
Using the expression 7 V = Psat ·R·G, the Model 2051 has
a dierential saturation power of 20 mW for the lowest
gain setting up to 0.7 µW for the highest gain setting.
At other wavelengths where the responsivity is lower,
the saturation power increases inversely with response
factor.
Note:
Note:

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Models 2051 & 2053Frequency Response and Noise •13
Frequency Response and Noise
Measuring Bandwidth
The frequency response and noise characteristics of
the adjustable photoreceiver depend on the selected
gain. The gures beginning on page 16 give the typical
frequency response and noise behavior for the
photoreceivers at each of the gain settings. The
frequency response of the transimpedance gain is
plotted using the expression
20·log[Gain(ƒ)/Gain(0)],
whereƒis the frequency and Gain(0) is the gain at DC.
The photoreceiver’s bandwidth is dened as the
frequency where the gain has decreased by 3 dB, or a
factor of .
Measuring Noise
The photoreceiver noise is characterized using the
noise equivalent power (NEP), which is a measure of
the weakest optical signal that the photoreceiver can
detect. The NEP is the optical power which will
produce a signal-to-noise ratio of 1 in a 1-Hz
bandwidth. The minimum detectable optical power
can be found using the relationship
Minimum Optical Power = NEP · ,
whereBW is the bandwidth. Note that NEP is a
wavelength-dependent quantity that changes with the
photodetector’s responsivity.
2
BW

esioNdnaesnopseRycneuqerF•41
Another way to characterize the noise is with the
photocurrent noise (In), which is related to NEP by
In= R · NEP,
whereRis the photodetector’s responsivity (in A/W).
The photocurrent noise is independent of wavelength
because it gives the noise of the photoreceiver with the
photodetector’s responsivity factored out.
To characterize the noise of the photoreceiver, the
output electrical noise spectrum is measured with a
spectrum analyzer. This voltage noise spectrum is
converted to an equivalent optical photocurrent noise
by dividing the voltage noise by the transimpedance
gain (V/A). The photocurrent noise,In(ƒ), has units of
pA/ and is plotted in Figure 3 and Figure 4 using
the expression20·log[In(ƒ)/1 A].
Calculating NEP
The noise equivalent power (NEP) can be calculated by
dividing the photocurrent noise by R, the detector’s
responsivity (see page 6).
From DC to 150 kHz the average photocurrent noise
for the Model 2051 on the high gain setting is about
0.34 pA/ , corresponding to an average NEP at
900 nm of 0.68 pW/ . The integrated noise
equivalent power from DC to 150 kHz is then obtained
by multiplying the average NEP by , the square
root of the bandwidth.
Theexpression BW = 2πƒ3-dB/4 for a one-pole low-
pass lter is useful for calculating the equivalent noise
bandwidth. Using the high-pass lter set 1 decade
below the low-pass cuto reduces noise-equivalent
bandwidth byapproximately 10 %. For the Model 2051
with a 3-dB bandwidth of 150 kHz, the equivalent
noise bandwidth is 235 kHz. This gives an optical noise
equivalent power of about 330 pW, so the minimum
detectable optical signal at 900 nm (with a signal-to-
noise ratio of 1) for the Model 2051 on the highest gain
Hz
Hz
Hz
BW

Models 2051 & 2053Frequency Response and Noise •15
setting is 330 pW when operating at full detector
bandwidth.
You can further improve your signal-to-noise ratio by
using optical modulators or choppers with lock-in
ampliers to limit the detection bandwidth. Using
such techniques you can reduce equivalent bandwidth
to 1 Hz or less.
Calculating Output-Voltage Noise
The output-voltage noise can be calculated from
G · R · NEP · ,
whereGis the gain (V/V),Ris the photodiode response
factor (V/mW), NEP is the average noise equivalent
power, and BWis the bandwidth. This gives an output
noise voltage for the Model 2051 on the high gain
setting of
(3x104V/V) · (0.35 V/mW) · (0.68x10-9 mW/ )
· =3 mVrms.
The Johnson noise at the input of a 100-MHz bandwidth
oscilloscope with 1-MΩ input impedance is 1.6 mVrms .
This is often the limiting factor in broadband measurements.
Summary
With the Model 2051 on the highest gain setting the
minimum NEP is 0.68 pW/ , and this yields an
output noise voltage of 3 mVrms . Viewed another way,
for operation at the peak responsivity wavelength of
900 nm and for the high gain setting, you will achieve a
signal-to-noise ratio of unity if the input power is
330 pW.
For the Model 2053 with an InGaAs photodiode, the
NEP at peak response wavelength of 1500 nm is
0.34 pW/ over the 150-kHz bandwidth. The full
BW
Hz
2π
4
------ 150 103Hz×
.
Hz
Hz

esioNdnaesnopseRycneuqerF•61
bandwidth signal-to-noise ratio of 1 is achieved
around 120 pW.
Note that this assumes operation without any post-
photoreceiver ltering and with the full photoreceiver
bandwidth. By using the built-in electronic band-pass
lter or an optical chopper and a lock-in amplier, the
receiver can detect signicantly weaker optical signals.
Performance Data for Frequency Response
The 3-dB frequency bandwidth is dened as the
frequency where the photoreceiver’s transimpedance
gain has decreased by a factor of . The typical
frequency responses for the Model 2051 and Model
2053 are shown in the following gures.
Figure 3:
Typical
frequency
response for
Model 205X at
each gain
setting
2
Gain Setting=1
-15
-12
-9
-6
-3
0
3
0.01 0.1 1 10 100
Frequency (MHz)
Normalized Gain (dB)
x1
x3
Gain Setting=10
-12
-9
-6
-3
0
3
0.01 0.1 1 10 100
Frequency (MHz)
Normalized Gain (dB)
x1
x3

Models 2051 & 2053Frequency Response and Noise •17
Gain Setting=102
-15
-12
-9
-6
-3
0
3
0.01 0.1 1 10 100
Frequency (MHz)
Normalized Gain (dB)
x1
x3
Gain Setting=103
-6
-3
0
3
11.010.0
Frequency (MHz)
Normalized Gain (dB)
x1
x3
Gain Setting=104
-6
-3
0
3
11.010.0
Frequency (MHz)
Normalized Gain (dB)
x1
x3

esioNdnaesnopseRycneuqerF•81
Performance Data for Noise
Figure 4 shows the typical noise spectrum expressed as
photocurrent noise for Model 205X photoreceivers on
the highest gain setting.
To derive the receiver’s Noise Equivalent Power (NEP),
divide the photocurrent noise by the photodiode
responsivity. To convert to output voltage noise (RMS),
multiply the photocurrent noise by the gain setting
from the 205X front label, then by 630 V/A (the scaling
factor between the gain setting labels and the actual
amplier transimpedance gain).
For example, the output voltage noise (RMS) for Model
2053 in the 3x103setting is approximately:
0.34 pA/ x 3 x 103x 630 V/A = 0.65 µVrms/.
For the 700 kHz of amplier bandwidth in the 3x103
gain setting, the equivalent noise bandwidth is:
( 2 x π/4 ) x 700 x 103Hz = 1.1 MHz,
so the predicted output noise voltage is approximately
0.65 µVrms/ x = 0.7 mVrms.
Because the NEP is listed at the highest gain setting,
some additional considerations add to the NEP at lower
gain settings. First, the noise spectrum (Figure 4) is not
at, rising at frequencies above 100 kHz. This
contributes an extra 20% to the output noise voltage in
the 3 x 103
setting compared to 3 x 104 . Also, as the
output noise voltage approaches 1 mVrms , the Johnson
noise limit of your measurement instrument will
become important. Note that the Johnson noise for an
oscilloscope with 100-MHz bandwidth (assuming
perfect roll o) and 1-MΩinput impedance is
1.2 mVrms.
Hz Hz
Hz 1.1 106
×Hz

Models 2051 & 2053Frequency Response and Noise •19
Figure 4:
Typical noise
spectrum for
Model 205X
Noise (pA/ Hz)
205XOutput Noise Current
0.20
0.25
0.30
0.35
0.40
0 10 20 30 40 50 60 70 80 90 100
Frequency (KHz)
Spec
Gain = 3 x 104

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