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Series G PDM
Series G Unamplified
Single Photodetectors
for light levels
of 0.1 mW and higher

Series F PDM
Series F Amplified Single Photodetectors
with new improved amplifiers
for light levels down to nanowatts and below

Series F Differential PDM
Series J Amplified
Differential Photodetectors

like Series F single detectors,
but only the difference is amplified

New Series F Power Supply with A-B switch
Power Supply
for DC coupled PDMs
and all Differentials

International Orders
International Order Policies



Martin, Froeschner & Associates

Series F Fast Compact Photodetector Modules

Newly Revised Amplifier Options

Even Higher Gain with Four Stages of Amplification in the same Compact Module Size

Bandwidths to 12 GHz
Sensitivities to over thirty million V/W
And a new Ultra-Low Noise Series with Noise Figures as low as 0.9 dB

Faster, more compact, and cheaper than our Award Winning Series 99 Photodetectors.

A new line of inexpensive and compact fiber-coupled photodiode modules simplify capturing fast transient light signals for analysis. These devices are intended to approximate as closely as possible, a length of fiber optic cable that can be connected directly onto the input jacks of your oscilloscope or other electronic data acquisition device. Conversion of the optical signal to electronic current and voltage occurs at the last possible moment, within a mm or so of the input jacks of your scope. Co-ax cable and the problems of reflections, termination loads, phase distortion and so forth are totally eliminated. The devices are extremely compact and rugged, taking up about as much room as a typical BNC terminator

These modules are available with a broad range of configurations, connector and fibre options, photodiode and amplifier choices as detailed below.

0.65" (16mm) diameter by 1" to 1.7" (25 to 43 mm), excluding connectors and optical fiber
Construction: machined from solid 6061-T6 Aluminum, internal components potted in epoxy resin
Power: shielded four-conductor cable to External Power Supply.

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Optical Fiber and Connector

We will build your modules with whatever optical fiber, cable and connectors you specify. We normally stock single-mode 9/125 m and both 50/125 m and 62.5/125 m multimode fiber with 0.9mm polymer buffer and 3mm Kevlar jacket. Other types such as 100/140 m are available. The fiber to photodiode connection is angle polished for low (-45dB) back reflection.

The input end of the optical fiber will be fitted with whatever type of optical fiber connector you desire. The range of normal options include: none, i.e. a bare fiber pigtail, 2 mm ceramic ferrule only, NTT-FC, SC, ST and SMA. The fiber end itself will be polished to any of the standard specifications: flat, UPC, or APC (8o). If you need something else, just specify so on the Order Form.

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Optional Light Collecting Optics

If the signal you want to analyze is in the form of a beam in free-space we can provide light collecting optics instead of or in addition to the optical fiber connectors described above. A 6 mm diameter fixed focus aspheric lens assembly is available. We also offer a micro-alignable fixture with 27 mm aperture focusable achromatic lens. Precision fine thread adjustments allow you to maximize the coupling of the incoming beam into the fiber. The unit is also directly compatible with "micro-rail" optical component systems made by Newport, Melles-Griot, ThorLabs and others and is "C" threaded for compatibility with Edmund Scientific's modular component line. Finally, large aperture catadioptric systems for collecting light from weak, distended or distant sources can be provided. Details available upon inquiry.


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Photodiode Selection

graph of Responsivity vs Wavelength of PhotodiodesThe two major considerations in selecting the photodiode for your application are spectral response and speed. Photodiodes based on different semiconductor materials have, in general, different ranges of light wavelength to which they are most sensitive.

For example, Silicon based diodes are most sensitive in the 400nm (nearly UV) to 1000nm (near IR) spectral range and cover the visible well. InGaAs is relatively insensitive to visible light but responds well to the IR used in information systems.

The intrinsic speed of the photodiode is also determined by the semiconductor material. The higher electron mobility in InGaAs allows response times which are simply not attainable with Si. Our latest GaAs model offers unprecedented speed in the visible range. Other factors which might be important to your needs, such as Dark Current and Capacitance are also listed in the table on Photodiode Specifications. The maximum allowable input optical power is 10 mW.

The photodiode in all our modules is reverse biased to minimize intrinsic capacitance for maximally fast response.


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Photodiode Specifications

Specifications are listed for the usual photodiodes. Others are available, call or write for details.






Spectral Range

450-870 nm

850-1700 nm

850-1700 nm

950-1650 nm


0.60 A/W at 850

0.9 A/W@1550

0.9 A/W@1550

0.9 A/W@1550

Bandwidth (-3db)

10 GHz

3.5 GHz

>7.5 GHz

>10 GHz

Rise/Fall Time

<35 ps

100 ps

<50 ps

<35 ps


0.2 pF

0.6 pF

0.17 pF

<0.2 pF

Active Area

75 m dia.

100 m dia.

50 m dia.

30 m dia.

Dark Current

<0.3 nA

<0.4 nA

<0.4 nA

<0.4 nA

Fiber Compatibility

up to 62.5 m

up to 100 m

up to 50 m

single mode

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Transimpedance Amplifier Options and Specifications

When the light level gets below the mW regime, the expected signal is uncomfortably near the noise floor of most systems. In order to get acceptable signal levels from very low light levels the current from the photodiode must be amplified. In the Series F modules we use the latest microwave GaAs and InGaP technology in Darlington configurations. This allows much higher performance than the classical configuration using an Op-amp with feedback resistance. Expected signal levels can be estimated as described below, Estimation of Signal Level. Note that these amplifiers are built into the Photodetector module body, closely coupled to the photodiode and the electrical output for maximum performance. They are not a separate component.

We have recently completely revised our transimpedance amplifier line, using components from new sources with higher bandwidth, better gain flatness and lower noise figures than before. These new amplifier options are available, as before, in single stage versions with true DC coupling, and in AC coupled multi-stage configurations. We are also now offering a new series with extremely low Noise specifications and very high overall gain.

Other amplifier options are available. Let us know what you need and we will do our best to devise a configuration that meets your needs.

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True DC Coupling with Offset Null

These amplifiers work all the way down to zero Hertz, i.e. CW, and are useful where the absolute value of light intensity must be measured as opposed to mere variations in intensity. They use two identical amplifiers, one driving the center conductor of the output connector with the amplified photodiode signal, the other driving the outer or ground conductor of the output with a DC signal to compensate for the DC offset inherent with Darlington pair configured amplifiers. This DC Offset can be varied to null out any background due to dark current or other sources. We recommend that our Power supply with provision for this Offset Null feature be used with these amplifiers.


Bandwidth (-3db)


Gain Flatness

Noise Figure, NF

Output Power (P1dB)

Mod 5D

DC to 12 GHz

200 volts/amp

1.5 dB, 100 MHz to 12 GHz

4.9 dB @ 3 GHz

14.5 dBm

Mod 8D

DC to 7 GHz

300 volts/amp

2 dB, 500 MHz to 5 GHz

3.2 dB @ 2 GHz

12.4 dBm

Mod 4D

DC to 2.8 GHz

2,500 volts/amp*

0.8 dB, DC to 2 GHz

2.6 dB @ 1.5 GHz

-2 dBm

The Transimpedance specification for Mod 4D amplifier given above assumes high impedance termination. Due to the relatively low output power of this amplifier, the Transimpedance when terminated into 50 ohms is approximately one-half of the specified value. This applies only to the Mod 4D amplifier, all others will drive 50 ohm as well as high Z termination with no change in specifications

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Highest Performance, AC Coupled

We have recently greatly increased the amplification and overall performance available in the AC coupled
Photodetector Modules. Advanced fabrication techniques now allow us to package four stages of amplification in the same module body as before with no increase in size. These new single and multi-stage AC coupled transimpedance amplifiers provide bandwidths up to 12 GHz, with excellent Gain Flatness. Overall conversion gains over 10,000 volts/watt allow detection of sub micro-watt signals with bandwidths still at nearly 6 GHz and above. For lower Noise and even higher gain, see below.



Bandwidth (-3dB)


Gain Flatness

Noise Figure, NF

Output Power (P1dB)

Mod 5A

30 kHz to 12 GHz

200 volts/amp

1.5 dB, 100 MHz to 12 GHz

4.9 dB @ 3 GHz

14.5 dBm


40 kHz to 8.4 GHz

750 volts/amp

3 dB, 100 MHz to 8 GHz

5.7 dB @ 3 GHz

14.5 dBm

Mod 555A

50 kHz to 7 GHz

2,700 volts/amp

4 dB, 100 MHz to 6 GHz

5.9 dB @ 3 GHz

14.5 dBm

Mod 5555A

60 kHz to 5.9 GHz

10,800 volts/amp

5 dB, 100 MHz to 5 GHz

5.9 dB @ 3 GHz

14.5 dBm

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Low Noise, High Gain, AC Coupled

These have been long-standing favorites. The Mod 4 series of single and multi-stage AC coupled transimpedance amplifiers provide bandwidths up to 2.8 GHz, with excellent Gain Flatness and low frequency response down to 30 kHz. Overall conversion gains of over a million volts/watt allow detection of sub micro-watt signals. For lower Noise and even higher gain, see below.


Bandwidth (-3dB)


Gain Flatness

Noise Figure, NF

Output Power (P1dB)

Mod 4A

30 kHz to 2.8 GHz

2,500 volts/amp*

0.8 dB, 50 MHz to 2 GHz

2.6 dB @ 1.5 GHz

-2 dBm


40 kHz to 2.8 GHz

7,500 volts/amp

1.5 dB,50 MHz to 2 GHz

2.78 dB @ 1.5 GHz

12.4 dBm

Mod 442A

50 kHz to 2.0 GHz

200,000 volts/amp

2 dB, 50 MHz to 2 GHz

2.68 dB @ 1.5 GHz

12.4 dBm

Mod 444A

50 kHz to 1.8 GHz

1,600,000 volts/amp*

2 dB, 50 MHz to 2 GHz

2.68 dB @ 1.5 GHz

-2 dBm

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Lower Noise, Higher Gain, AC Coupled

We are introducing a new line of transimpedance amplifier options to replace the venerable but obsolescent Mod 4 Series, for those who need extremely low noise levels for detection of signals down in the nano-watt regime. The principle difference between these and the older Mod 4s above are lower Noise Figure and Higher Gain at comparable bandwidths, but with a somewhat higher low frequency cutoff.


Bandwidth (-3dB)


Gain Flatness

Noise Figure, NF

Output Power (P1dB)

Mod 9A

500 MHz to 5 GHz

600 volts/amp

1.6 dB, 0.5 to 4.0 GHz

1.4 dB @ 1 GHz

20 dBm

Mod 99A

700 MHz to 3.5 GHz

7,400 volts/amp

2 dB, 0.5 to 3.0 GHz

1.4 dB @ 1 GHz

20 dBm

Mod 999A

850 MHz to 2.9 GHz

90,000 volts/amp

2 dB, 0.5 to 2.5 GHz

1.4 dB @ 1 GHz

20 dBm

Mod 9999A

1 GHz to 2.5 GHz

1,100,000 volts/amp

2 dB, 0.5 to 2.5 GHz

1.4 dB @ 1 GHz

20 dBm

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Ultra - Low Noise, Even Higher Gain, AC Coupled

And for those who need extremely low noise levels for detection of signals down in the sub-nano-watt regime, these amplifiers are available in four versions with Noise Figures below 1 dB, bandwidths as high as 2.2 GHz, excellent Gain Flatness and Transimpedance gains to over thirty million volts/watt



Bandwidth (-3dB)


Gain Flatness

Noise Figure, NF

Output Power (P1dB)

Mod 7A

20 MHz to 2.2 GHz

1,500 volts/amp

1.5 dB, 0.4 to 1.8 GHz

0.9 dB @ 0.9 GHz

22 dBm

Mod 77A

30 MHz to 1.6 GHz

45,000 volts/amp

2.5 dB, 0.4 to 1.4 GHz

0.9 dB @ 0.9 GHz

22 dBm

Mod 777A

35 MHz to 1.3 GHz

1,350,000 volts/amp

3.5 dB, 0.4 to 1.0 GHz

0.9 dB @ 0.9 GHz

22 dBm

Mod 7777A

40 MHz to 1.0 GHz

40,000,000 volts/amp

4.5 dB, 0.4 to 1.0 GHz

0.9 dB @ 0.9 GHz

22 dBm

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Keep in mind that the transimpedance amplifier is an option. If your light levels are adequate, use the basic configuration Series G unamplified (but biased) photodiode without the added current drain, cost and potential additional noise of an amplifier.

We also make the Series J version of all of these amplified modules, with dual optical inputs. In these Differential modules the two photodiodes are arranged in a totem-pole as in TTL logic. The amplifier input is connected at the mid-point node between the two photodiodes and thus sees only the difference between the two photodiode signals. Skip to the Series J page for details.

Series F Mod 11A Photodetector with Power Supply

Series J Amplified Differential Photodetector with Power Supply

Estimation of Signal Level

You can estimate the signal level (voltage) that you can expect to see, for your light intensity, directly from the Responsivity as shown in the graph above and the amplifier Transimpedance given in the tables above, from:

V [volts] = I [watts] Responsivity [amps/watt] Transimpedance [volts/amp]

where V is the output signal, I is the input light intensity.

Note that since the Responsivity of InGaAs is very nearly 1, the Transimpedance figures can be thought of directly as volts per watt of optical input in systems with InGaAs photodiodes.

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Noise Specifications and Measurements

Measurements of the noise spectrum have been made by independent labs on several of our earlier systems. In all measurements the results were consistent with or better than the published specifications.

An InGaAs-2 Mod1D with DC Offset Null contributed about 1.5mV rms over 20GHz with power on to both amplifiers and the photodiode and no light input. (The scope by itself had an intrinsic noise floor of about 1.2mV rms.) Calculations show this to be consistent with the Noise Figure specified below. The equivalent optical noise density at the input is about 50pW Hz -1/2. An AC coupled InGaAs-2 Mod2A system tested at one of the National Laboratories showed a 0.3mV rms noise floor, also consistent with the Noise Figure. The equivalent optical input noise density is about 30pW Hz-1/2. This system reliably receives digital data at 2.5Gb/s with light levels as low as a few microwatts.

Our latest amplifier models have even better Noise specifications, as well as higher Gain, higher Bandwidth and improved Gain Flatness.

The noise from the photodiodes themselves is several orders of magnitude below that of the amplifiers and may be ignored.

In general, we have found that the noise contributed by our amplified photodiode systems is below or at most comparable to the intrinsic noise floor of most high speed oscilloscopes and digital data acquisition systems. Our customers have told us that they are the best they have ever seen.

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Output Electrical Connector

Electronic output connector choices include BNC, TNC, SMA and SMC in either gender. Wiltron-K, 7/16 and others are available at some extra cost. Please note that BNC connectors are not recommended above 2 to 4 GHz. If you need something really unusual, specify on your Request for Quotation or call to discuss your needs.

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Input Coupling Option to Prevent Saturation

The photodiode is normally connected directly to the input terminal of the first stage amplifier. In some situations, such as the detection of a small signal riding on a large DC component, the DC component might saturate the first stage amplifier. This can be avoided by capacitively coupling the photodiode to the amplifier input, so that the DC component has no effect. However, in this configuration the photodiode must have a load resistor of about 50 ohms in order to maintain its performance and since this parallels the amplifiers input impedance, the overall transimpedance gain will be reduced by roughly one-half.

To specify this Option, add another A to the Model number, for example, Mod 55AA.

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These modules are designed to be mounted directly onto the input jack of your scope. When used this way there is no coax cable to cause reflections so terminating with exactly 50 ohms is not necessary. The output impedance of the amplified modules is already low so you may set the input impedance of your scope to 1Mohm. The amplifiers will drive a 50 ohm load but there may be a reduction in signal level for certain amplifier configurations as explained above.

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Power Considerations

The amplified Series F modules are powered through a shielded multi-conductor cable. This cable is fitted with a connector which is compatible with the M,F&A Power Supply. Any power supply is a potential source of noise. The M,F&A Power Supply provides noise free power to the photodiode and amplifiers from Nickel metal hydride batteries which are re-charged when the photodetector module is not in use. When the photodetector module is active, the system is completely disconnected from the external AC source.

Amplified versions which are DC coupled would have an output offset bias of several volts when the photodiode is dark, due to transistor biasing. This offset is eliminated with the Offset Null configuration which uses a second matched reference amplifier to drive the ground side of the output connector. A multi-turn precision pot in the M,F&A Power Supply controls the input to this second amplifier so that any residual offset due to amplifier mismatch, photodiode dark current or background light can be trimmed out.

The latest versions Mod5, Mod 7 and Mod 9 can be powered by a simple 5v DC Laboratory Grade Power Supply. Current drain is about 150mA per stage. The voltage should be well regulated and never exceed 6.0 volts.

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Series F Amplified Photodetector Module Summary and Prices

Input Optical Connector:


         2.5mm ceramic ferrule







(compatible with flat, PC, and SPC)


         APC 8 degrees

         other ______________

Optical Cable:

         9/125 m

         50/125 m

         62.5/125 m



         0.9mm buffer only

         3mm Kevlar and Polymer over 0.9mm buffer



         1 meter (standard)


Light-Collection Optics:


         6mm fixed aspheric ($225)

         alignable Micro-Rail and "C" thread compatible ($695)

         Large Aperture (inquire)

Photodiodes :

         GaAs, 450-870nm, 10 GHz ($1,095)

         InGaAs-1, 850-1700nm, 3.5 GHz ($895)

         InGaAs-2, 850-1700nm, >7.5 GHz ($995)

         InGaAs-3, 950-1650nm, >10 GHz ($1,095)

Amplifier Options:

True DC Coupling, with Offset Null

         Mod 5D, 0 to 12 GHz, 200 ohms ($675)

         Mod 8D, 0 to 7 GHz, 300 ohms ($675)

         Mod 4D, 0 to 2.8GHz, 2,500 ohms ($775)

High Performance, AC Coupled

         Mod 5A, 12 GHz, 200 ohms ($375)

         Mod 55A, 8.4 GHz, 750 ohms($550)

         Mod 555A, 7 GHz, 2,700 ohms ($725)

         Mod 5555A,.5.9 GHz, 10,800 ohms ($900)

Low Noise, High Gain, AC Coupled

         Mod 4A, 2.8 GHz, 2,500 ohms ($375)

         Mod 42A, 2.8 GHZ, 7,500 ohms ($550)

         Mod 442A, 2 GHz, 200,000 ohms($725)

         Mod 444A, 1.8 GHz, 1,600,000 ohms ($725)

Lower Noise, Higher Gain, AC Coupled

         Mod 9A, 5 GHz, 600 ohms ($475)

         Mod 99A, 3.5 GHz, 7,400 ohms ($650)

         Mod 999A, 2.9 GHz, 90,000 ohms ($825)

         Mod 9999A, 2.5 GHz, 1,100,00 ohms ($1,000)

Ultra Low Noise, Higher Gain, AC Coupled

         Mod 7A, 2.2 GHz, 1,500 ohms ($475)

         Mod 77A, 1.6 GHz, 45,000 ohms($650)

         Mod 777A, 1.3 GHz, 1,350,000 ohms ($825)

         Mod 7777A, 1.0 GHz, 40,000,000 ohms ($1,000)

Output Electronic Connector:







         male plug (as in the photos above)

         female jack

Input Coupling Option:


         capacitive, non-saturating (additional A to Model Number)


Standard External Power Supply:

         12volt rechargeable NiMH with EMI/RFI shielding ($375)

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How to Order

We will build your Photodetectors to your specifications. The price of your detector is simply the sum of the prices of the chosen specified options. Email us your specifications from the list under Summary and Prices above. We will return a formal quotation to confirm your specifications and expected delivery time. Quantity discounts are available, send a Request for Quotation.

Please note that these modules contain technology at the leading edge of the state of the art. Prices and specifications are subject to change.


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Martin, Froeschner & Associates
14300 Mines Road, Livermore, California, 94550

tel: (+1) 925 989 4930
fax: (+1) 925 449 4647


  Latest update June 2016


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Contact Us:

tel: +1 925 989 4930
fax: +1 925 449 4647


Martin, Froeschner & Associates
14300 Mines Road
Livermore, California

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