USER’S GUIDE
12-GHz Amplified
Free-Space Photoreceivers
Models 1567 & 1577
Including low-frequency “-LF” Options
These photoreceivers are sensitive to electrostatic
discharges and could be permanently damaged if
subjected even to small discharges. Ground yourself adequately prior to handling these receivers or
making connections. A ground strap provides the
most effective grounding and minimizes the
likelihood of electrostatic damage.
®
NEW FOCUS, Inc.
®
2630 Walsh Ave. • Santa Clara, CA 95051-0905 • USA
phone: (408) 980-8088 • Fax: (408) 980-8883
e-mail: [email protected] • www.newfocus.com
Warranty
New Focus, Inc. 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.
Copyright 1999, New Focus, Inc. All rights reserved.
The
symbol and NEW FOCUS, Inc. are registered trademarks
of NEW FOCUS, Inc.
Document Number 156701 Rev. A
Contents
Operation
5
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Handling Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Microwave connection and set-up . . . . . . . . . . . . . . . . . . . . . . .
Connecting the Power Supply and Bias . . . . . . . . . . . . . . . . . .
Aligning the Photodetector to the Optical Input. . . . . . . . . .
Troubleshooting
5
6
6
7
8
11
Testing the Photodiode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Checking the DC-Offset Voltage. . . . . . . . . . . . . . . . . . . . . . . . 11
Basic Optical Test. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Checking Allignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Characteristics
13
Photoreceiver Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Bias-Monitor Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Responsivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Customer Service
15
Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Appendices
17
Appendix I: Inside the Photoreceiver Module. . . . . . . . . . . . 17
Appendix II: Focusing on the Detector . . . . . . . . . . . . . . . . . . 18
Appendix III: Microwave Connectors . . . . . . . . . . . . . . . . . . . 20
12-GHz Photoreceivers
Contents • 3
4 • Contents
NEW FOCUS, Inc.
Operation
Introduction
High-speed measurements down to a few microwatts
are easy with the Models 1567 and 1577 free-space
photoreceiver modules. These modules convert
optical signals to electronic signals, in effect giving an
optical input to every high-speed/high-frequency
instrument in your lab. The module’s small size makes
it easy to find space for it on your optical table or you
can connect it directly to your test instrument.
In both models, the InGaAs Schottky photodiode is
located somewhat off-center of the glass window,
away from the K-connector output. For proper
microwave performance, the optical beam must be
focused on the 25-µm Schottky diode. Figures 1 and 2
show the front, side, and rear views of the
photoreceiver and bias-supply modules.
Figure 1:
Models
1567 & 1577
photodetector
housing
0.18 (4.5) mounting-hole
center to detector center
on opposite side
0.50
0.17
0.22 (5.5) housing
to detector
0.19 (4.7) window
to detector
0.03 (0.8) window
thickness
0.75 (19.1)
0.30 (7.6)
0.75
(19.1)
0.31
2-56 (M2) thd
2x 8-32 (M4) thd
Connecting cable
to bias supply
not shown
12-GHz Photoreceivers
0.31 (8.0)
Output K-connected
Operation • 5
Figure 2:
Models
1567 & 1577
bias housing
Photoreceiver
connector
Bias monitor port
output is equal to photodiode
current times 1000 ohms, for
one millivolt per microamp
2.00 (50.8)
Power connector
1.00 (25.4)
Battery Check Button.
When depressed, bias
voltage is applied to
bias-monitor port
Power Switch
1XX7 Bias Supply
XX-GHz Photodetector
Off
2.00
(50.8)
On
Batt
Chk
Bias
Monitor
1mV/µA
NEW FOCUS
Made in USA
Remove two screws
to replace 9-V battery
1.60 (40.7)
0.56 (14.2)
2.25 (57.1)
Handling Precautions
Whenever handling the photoreceiver, make sure to
follow these precautions:
•
Prior to handling the detector or making
connections, be sure to ground yourself
adequately—even small electrostatic discharges
could permanently damage the detector. A ground
strap provides the most effective grounding and
minimizes the likelihood of electrostatic damage.
•
Do not over torque the microwave K-connector.
Excessive torque can damage connectors.
Microwave connection and set-up
1. Due to the small size of the detector’s active area,
bolt the detector housing to a fine-positioning
device such as the New Focus Model 9064 translation stage or to any x-y-z adjustment stage that is
compatable with 8/32" (M4) screws.
2. Connect the photoreceiver module’s microwave
connector to a test instrument that has a 50-Ω
input, such as an oscilloscope or spectrum
analyzer, or to another 50-Ω load. If necessary, use
a high-frequency cable such as the New Focus
6 • Operation
NEW FOCUS, Inc.
Model 1227 (best performance is achieved without
a cable).
For the low-frequency (“-LF”) version, be sure to include
the DC block between the receiver and the test instrument
to prevent possible damage to the equipment.
3. To avoid connector damage and signal distortion,
be sure that the cable and the instrument you
intend to connect to the module have compatible
connectors. See page 20 for a list of compatible
connectors.
Connecting the Power Supply and Bias
1. Prior to handling the detector, ground yourself
with a grounding strap to prevent electrostatic
damage to the receiver.
2. There are two gold “Microtech” connectors on the
bias housing. The one on the rear panel is for
supplying the bias to the detector housed in the
separate package. The connector on the side of the
bias housing is for the ±15 V from the power
supply. It is not physically possible to accidentally
mate the bias connector with the ±15-V power
supply, and vice versa.
3. Connect the power cable to the power supply. Two
power cables were included with the receiver; use
the appropriate cable for your power supply:
Connecting to a New Focus power supply: Use
the cable with the two Microtech connectors.
Connect the cable to one of the power supply’s
300-mA outputs.
Connecting to another power supply: Use the
cable with the Microtech connector on one end
and three banana plugs on the other end. Be
careful to connect the banana plugs to the power
supply as follows; connect the red plug to a wellregulated, +15-V, 200-mA source; connect the
12-GHz Photoreceivers
Operation • 7
black plug to a -15-V, 200-mA source; connect the
green plug to the common ground of the two
sources.
4. Connect the other end of the power cable to the
connector on the side of the bias housing.
5. Plug the cable from the detector housing into the
microconnector on the rear of the bias housing.
6. Turn on the power supply.
7. Turn on the photoreceiver using the switch on the
bias housing.
8. Connect the bias-monitor port to a voltmeter.
9. Press and hold the Batt Chk button and observe the
bias monitor output.
The regulated positive voltage is applied to the
bias-monitor SMA connector. A reading of 9 V
indicates proper connection.
10. Release the Batt Chk button and observe the
voltage level on the voltmeter. This voltage is the
DC offset plus dark current. This dark voltage
should be less than 15 mV.
Note:
If you are coupling light into a fiber, you can optimize the
coupling by attaching a voltmeter to the bias-monitor port and
monitoring the photocurrent.
Aligning the Photodetector to the
Optical Input
Method 1: Defocusing
1. Before placing the detector in the optical beam,
ensure that the optical power is within specified
limits (see page 13).
2. Position the module on the x-y-z adjustment stage
in front of the focusing lens. (For a discussion on
8 • Operation
NEW FOCUS, Inc.
how to choose the proper lens, see “Appendix II:
Focusing on the Detector” on page 18.)
3. Once the module has been roughly positioned in
front of the lens and all of the RF connections have
been made, connect a voltmeter to the bias
monitor output and turn it on. (The voltage
displayed when no light is striking the detector is
an electrical offset voltage and dark current.)
4. With the detector slightly out of focus so as to
increase the spot size in the plane of the detector,
move the detector slowly back and forth while
watching the voltmeter reading.
5. The moment the voltmeter reading increases by
5 mV or more, stop the coarse adjustment and use
a fine adjustment screw to adjust the x-y position
and the focus to maximize the voltage reading. A
voltage reading more than 20 mV above the offset
should be sufficient for observation of cw signals
on a spectrum analyzer.
6. As soon as the actual RF signal is observable, this
should be optimized instead of the voltmeter
reading. With very low duty-cycle signals (off
much longer than they are on), the voltmeter
reading will be too low to be useful unless used
with a chopper wheel and a lock-in amplifier. The
bandwidth of the bias-monitor output is high
enough for use with a lock-in and chopper wheel.
Note:
It is possible to illuminate areas on the photodiode chip which
give “false” signals with very slow responses. It may be
necessary to search for the true active area, which will give the
expected high-speed response.
Method 2: Projection
1. Follow the first two steps in Method 1 except place
an optical flat before the lens where the optical
beam is well collimated (see Figure 5 on page 19).
Remember that a fairly good optical-quality flat is
12-GHz Photoreceivers
Operation • 9
required to prevent introducing aberrations which
would limit your focusing ability.
2. Place the flat at an angle so that you can
conveniently observe the reflection from the
photodiode surface on a white piece of paper.
3. Bring the module into focus so that you get a clear
image. Referring to the illustration in Figure 5
(page 19), center the photodetector in the image
and move the module so that the illuminated area
(and the image) becomes smaller. At this point you
should have a signal on the voltmeter.
4. Follow steps 4–6 in Method 1.
10 • Operation
NEW FOCUS, Inc.
Troubleshooting
Testing the Photodiode
The photodiode can be damaged by electrostatic
discharge or excessive optical power, which can lead to
an increased dark (or offset) voltage. A damaged
photodiode can result in a degraded responsivity and
frequency/impulse response. See “Checking the DCOffset Voltage,” below.
Also, it is possible to illuminate areas on the
photodiode chips which give “false” signls with very
slow responses. See “Checking Allignment” on page 12
Other problems, such as a damaged amplifier, are
more difficult to diagnose. If the response from your
receiver is lower than you expect, contact New Focus
to arrange for a repair (see “Customer Service” on
page 15).
Checking the DC-Offset Voltage
1. With no light on the photodetector, turn the
detector on.
2. Use a voltmeter to measure the Bias Monitor
output voltage. This voltage is the DC offset plus
dark current.
3. If the output is >15 mV, then the detector is
probably damaged and will need to be returned.
If the output is <15 mV, then perform the Basic
Optical Test described on the next page.
12-GHz Photoreceivers
Troubleshooting • 11
Basic Optical Test
To quickly test the photodiode in your receiver, run
this simple DC optical test.
1. Turn the receiver on.
2. Using a voltmeter or oscilloscope, measure the
output voltage from the Bias Monitor on the front
panel of the bias supply.
With no light on the detector, the Bias Monitor
voltage should be <15 mV.
3. Illuminate the photodetector.
4. With the voltmeter or oscilloscope, you should
observe a DC output voltage.
If you know the optical power and wavelength,
you can calculate the expected output voltage
( Vout) using the expression: Vout = Pin • R • G, where
Pin is the input optical power (watts), R is the
photodetector’s responsivity (A/W), and G is the
bias-monotor port’s transimpedance gain, which
is equal to 1000 V/A.
If the output voltage is low, then contact New Focus to
arrange for a repair (see “Customer Service” on
page 15).
Checking Allignment
When searching for a signal with the adjustment stage,
it is possible to encounter local maxima which are not
the desired signal. These locations typically have a
weaker response which is much slower than 12 GHz or
30 ps. If you encounter such a signal, search elsewhere
for the true active area, which will give the expected
high-speed response.
12 • Troubleshooting
NEW FOCUS, Inc.
Characteristics
Photoreceiver Characteristics
Model #
Wavelength Range
1567
1577
950–1650 nm
400–1650 nm
3-dB Bandwidth
(low-frequency versions)
Rise Time
5 MHz–12 GHz
10 kHz–12 GHz
30 ps
30 ps
Max. Conversion Gain
220 V/W
74 V/W
Typical Max. Responsivity
0.6 A/W
0.2 A/W
Transimpedance Gain
370 V/A
370 V/A
50 Ω
50 Ω
Output Impedance
Minimum NEP
33
cw Saturation Power
2 mW
6 mW
Maximum Pulse Power
2 mW
6 mW
Detector Material/Type
Detector Diameter
Power Requirements
Optical Input
Electrical Output
12-GHz Photoreceivers
pW
----------Hz
100
pW
----------Hz
InGaAs/Schottky
25 µm
±15 V, <200 mA
Free Space
Wiltron K
Characteristics • 13
Bias-Monitor Characteristics
All Models
DC Gain
1 mV/µA
DC Offset (max.)
15 mV
Output Impedance
10 kΩ
Bandwidth
50 kHz
Responsivity
A graph of the typical and predicted responsivity of
the Models 1567 and 1577 photoreceivers is shown
below.
a
Responsivity
increases
from 0–0.52 A/W
over the range of
950–970 nm.
0.6
Responsivity, A/W
Figure 3:
Responsivity vs.
wavelength for
a) Model 1567
b) Model 1577
0.4
0.2
b
0.0
300
500
700
900
1100
1300
1500
1700
Wavelength, nm
14 • Characteristics
NEW FOCUS, Inc.
Customer Service
Technical Support
Information and advice about the operation of any
New Focus product is available from our technical
support engineers.
Engineers are on duty from 8:30–5:00 PST, Monday
through Friday (excluding holidays). For quickest
response, ask for “Technical Support” and know the
model number for your receiver. The model number is
printed on the front panel of the receiver.
Phone: (408) 980-8088
Fax: (408) 980-8883
Support is also available by email.
Email: [email protected]
We typically respond to email within one business day.
Service
In the event that your photoreceiver malfunctions or
becomes damaged, please contact New Focus for a
return authorization number and instructions on
shipping the unit back for evaluation and repair.
12-GHz Photoreceivers
Customer Service • 15
16 • Customer Service
NEW FOCUS, Inc.
Appendices
Appendix I: Inside the Photoreceiver Module
This simplified schematic of the photoreceiver and
bias circuitry is provided for your reference.
Figure 4:
Schematic of
the Models
1567 & 1577
photoreceiver
module
Photoreceiver
Module
Microwave
Output
Connector
Photodiode
–
+
Bias
Monitor
Plug
V
+
V
V
Socket
Batt
Chk
+
On/Off
+
V
-
(rear panel)
+
–
Bias
Module
12-GHz Photoreceivers
V
-
(side panel)
Appendices • 17
Appendix II: Focusing on the Detector
Each Model 1567 and 1577 photoreceiver consists of a
25-µm-diameter photodetector and two amplifier
chips. For optimal performance, the spot size of the
optical beam striking the detector should be 20 µm.
Tighter beam focus will result in excessive opticalpower density. Looser beam focus will result in
reduced detector efficiency and bandwidth
degradation. For a diffraction-limited Gaussian beam
the focal length of the focusing lens should be
d0D
f = --------2λ
where ƒ is the focal length, do is the focused beam
diameter (20 µm), D is the diameter of the collimated
beam striking the lens, and λ is the optical wavelength.
18 • Appendices
NEW FOCUS, Inc.
Figure 5:
Using a good
optical flat,
project the
reflected image
onto a sheet of
paper
Note:
Chip
The 1567 chip is mounted upside down, so the front side is
available only with >950 nm illumination.
Amplifier
Photodiode
InGaAs
12-GHz Photoreceivers
Appendices • 19
Appendix III: Microwave Connectors
The performance you obtain from the Models 15X7
photoreceivers depends largely on the instruments
you use to measure their outputs and how the
connections are made to the instruments.
Connect the male connector of the photoreceiver
directly to the female connector of the instrument or
to an intervening high-frequency coaxial cable. If you
use a cable, select a cable with sufficiently low loss in
the frequency range of interest. (For the low-frequency
version, be sure to include the DC block between the
receiver and the instrument.)
If you need to use an adapter, make sure it is designed
for your frequency range of interest. The following
table lists a few connectors and the frequency ranges in
which they may be used. For more information,
request Application Note 1.
Connector
Frequency Range
Compatibility
BNC
DC–2 GHz
——
SMA
DC–18 GHz
Wiltron K, 3.5 mm
3.5 mm
DC–34 GHz
SMA, Wiltron K
Wiltron K
DC–40 GHz
SMA, 3.5 mm
2.4 mm
DC–55 GHz
Wiltron V
Wiltron V
DC–65 GHz
2.4 mm
New Focus also offers the following adapters:
Model 1225 Male-SMA to Female-BNC
Model 1226 Female-SMA to Male-BNC
Model 1227 40-GHz Flex Cable, Female-K to Male-K
20 • Appendices
NEW FOCUS, Inc.