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Interferometer Systems
a new kind of VISAR


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


Series F Amplified
Single Photodetectors
for light levels down to nanowatts


Series F Amplified
Dual Differential Photodetectors
like Series F single detectors,
but only the difference is amplified


Power Supply
recommended
for DC coupled PDMs
and all Differentials


International Order Policies

Martin, Froeschner & Associates
Series F Amplified Dual Differential Photodetector Modules

Sensitivities to over a million V/W and Speeds to 10 GHz

Updated: June 2010

M,F&A's continuously improved Amplified Dual Differential Photodetector Modules allow detection of the difference between two optical signals at bandwidths up to 10 GHz and overall optical conversion gains of 15,000 volts/watt or more. They are perfectly suited for detection of the phase difference between two otherwise identical signals such as in range finding or in phase encoded communication protocols. Other applications include the detection of small optical modulations on a high power or unpredictably variable background. In these modules the background cancellation is done at the optical input stage before amplification, avoiding limitations due to amplifier saturation by the background signal.

These modules are available with the same broad range of photodiode and amplifier choices as our Award Winning Series 99 Photodetector Modules. The fully enclosed and potted modules may be used free-standing or mounted to a PC board. Fiber type, connector types, photodiode spectral range, and amplifier may be chosen from our list of standard options or specified by the customer. The result is a Dual Differential Photodetector Module optimized for your particular application.

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Optical Fiber and Connector

We will build your modules with whatever optical fiber, cable and connectors you specify. We stock single-mode 9/125microm and both 50/125microm and 62.5/125microm multimode fiber with 0.9mm polymer buffer and 3mm Kevlar jacket. Other types such as 100/140microm are available. Jacketing options include 0.9mm polymer buffer only or the usual 3mm Kevlar and polymer jacket. All fiber to photodiode connections are angle polished for low (-45dB) back reflection.

The input end of the optical fibers will be fitted with whatever optical fiber connections you desire. The range of normal options include: none, i.e. abare fiber pigtail, 2.5mm ceramic ferrule only, NTT-Fc, SC, St, and SMA. The fiber end itself will be polished to any of the standard specifications: Flat, PC, SPC, or APC(8 degrees). If you need something else, just specify so.

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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. The simplest is a 2mm diameter GRIN lens and ferrule assembly permanently fixed on the end of the fiber. For larger beams a 6mm diameter fixed focus aspheric lens assembly is available. We also offer a micro-alignable fixture with 18mm 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

The 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 photodiodes in all our receivers are 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.

	GaAs	InGaAs-1	InGaAs-2	InGaAs-3
Spectral Range	450-870 nm	850-1700 nm	850-1700 nm	950-1650 nm
Responsivity	0.3 A/W@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	40 ps	100 ps	<50 ps	<35 ps
Capacitance	0.2 pF	0.8 pF	0.17 pF	<0.2 pF
Active Area	200 microm sq.	100 microm dia.	60 microm dia.	30 microm dia.
Dark Current	<0.3 nA	<0.4 nA	<0.4 nA	<0.4 nA
Fiber Compatibility	any	up to 100 microm	up to 50 microm	single mode

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Transimpedance Amplifier Option

The amplfiers used in the Series F Dual Differential Photodetectors are hybrid bipolar high electron mobility technology in Darlington configurations. All amplifier options are available in AC coupled configurations. The Mod1A, 2A, and 4A are multi-staged and are availabe only in AC coupled configurations. The Mod1, 2, and 4 may be ordered in true DC coupled versions.

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Transimpedance Amplifier Specifications

The amplifier selection for Series F Amplified Dual Differential Photodetectors are listed below.

We have renamed the single stage detectors with a D for DC coupled and an A for AC coupled to simplfy specification and ordering.

True DC Coupling - Single Stage
DC with Offset Null

	Mod 1D	Mod 2D	Mod 4D
Bandwidth (-3dB)	DC to 10 Ghz	DC to 7 GHz	DC to 2.8 GHz
Rise/Fall Time	35 ps	50 ps	125 ps
Transimpedance	200 ohms	300 ohms	2,500 ohms
Noise Figure	5.3 dB @ 2GHz	4.7 dB @ 2GHz	2.6 dB @ 1.5GHz
Output Power (P1dB)	11.3 dBm	12.4 dBm	-2 dBm

AC Coupling - Single Stage

	Mod 1A	Mod 2A	Mod 4A
Bandwidth (-3dB)	DC to 10 Ghz	DC to 7 GHz	DC to 2.8 GHz
Rise/Fall Time	35 ps	50 ps	125 ps
Transimpedance	200 ohms	300 ohms	2,500 ohms
Noise Figure	5.3 dB @ 2GHz	4.7 dB @ 2GHz	2.6 dB @ 1.5GHz
Output Power (P1dB)	11.3 dBm	12.4 dBm	-2 dBm

M,F&A has added greatly increased the amplification available in the AC coupled Photodetector Modules. The new internal multi-stage AC coupled transimpedance amplifiers provide overall conversion gains as high as 60,000 volts/watt in two stages and over a million volts/watt in three stages, allowing detection of sub-microwatt signals.

Series F Mod 11A Photodetector with Power Supply

AC Coupling - Two Stage

	Mod 11A	Mod 22A	Mod 42A	Mod 44A
Bandwidth (-3dB)	30 kHz to 7 GHz	30 kHz to 5 GHz	30 kHz to 2.8 GHz	30 kHz to 2.0 GHz
Rise/Fall Time	50 ps	70 ps	125ps	175ps
Transimpedance	800 ohms	1,800 ohms	7,500 ohms	60,000 ohms
Noise Figure	6.00 dB @ 2 GHz	5.15 dB @ 2 GHz	2.78 dB @ 1.5 GHz	2.68 dB @ 1.5 GHz
Output Power (P1dB)	11.3 dBm	12.4 dBm	12.4 dBm	-2 dBm

AC Coupling - Three Stage

	Mod 111A	Mod 222A	Mod 422A	Mod 442A	Mod 444A
Bandwidth (-3dB)	30kHz to 6GHz	30kHz to 4.5GHz	30kHz to 2.6GHz	30kHz to 2GHz	30kHz to 1.76GHz
Rise/Fall Time	60 ps	75 ps	135 ps	175 ps	200 ps
Transimpedance	3,200 ohms	10,800 ohms	45,000 ohms	200,000 ohms	1.6 x 106 ohms
Noise Figure	6.16 dB @ 2 GHz	5.22 dB @ 2 GHz	2.81 dB @ 1.5 GHz	2.68 dB @ 1.5 GHz	2.68 dB @ 1.5 GHz
Output Power (P1dB)	11.3 dBm	12.4 dBm	12.4 dBm	12.4 dBm	-2dBm

Note: Due to the relatively low output power of the Mod 4 amplifier, those modules with an amplifier Model Number ending in 4 will have Transimpedances about one-half of the value specified above when driving a 50 ohm termination load. For example, the Mod 44A delivers approximately 60,000 volts/amp into a high impedance termination and about 30,000 volts/amp into 50 ohms. For all other models the specified values are valid for either Hi-Z or 50 ohm termination.

This technology is developing rapidly. Other options are available. If your needs are not met by the choices lisetd, please contact us with your requirements or specifications.

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Estimation of Signal Level

You can estimate the signal level (voltage) that you can expect to see, for your light intensity, directly from the of the photodiode and the Transimpedance of the amplifier, from the following relation:

Signal [volts] = (I₁ - I₂) [watts] • Responsivity [amps/watt] • Transimpedance [ohms]

where I₁ and I₂ are the light power levels of the two input signals.

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Noise Specifications and Measurements

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

An InGaAs-2 Mod1 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 up ^-1/2. An AC coupled InGaAs-2 Mod2 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 microW peak.

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 (about 1mV RMS) of most high speed oscilloscopes and digital data acquisition systems

 

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Output Electrical Connector

The standard output electronic connector is SMA male. If you need something different, just specify on the Order Form or call to discuss your needs.

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Internal and Output Coupling

The Mod 1A, 2A and 4A amplifiers are several stage systems which are capacitively coupled. The photodiode input and the output signal in modules using these amplifiers are also AC coupled through capacitors, normally 0.1 microF. The low frequency cutoff (-3dB) is about 30 KHz. Higher cutoff frequency may be requested on the order form.

Receivers using the Mod 1, 2 or 4 amplifiers may be ordered in a true DC coupled version.

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Packaging

These Receivers are normally packaged in a solid metal RF enclosure. Dimensions are approximately 1.5" square by 0.75" exclusive of connectors and cables. The free-standing version has an integral shielded power cable. the PC mountable version has solder lugs for the power connections as shown in the photo. We will attempt to meet any special packaging or environmental requirements.

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Output Electrical Connector

Electronic output connectors are SMA in either gender. If you need something other than SMA, specify on the Order Form or call to discuss your needs.

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Power Considerations

Any power supply is a potential source of noise. The M, F & A External Power Supply provides noise free power to the photodiode and amplifiers from gel-cell batteries which are charged when the differential optical receiver is not in use. When the differential photodetector is active, the system is completely disconnected from the external AC source, and power is provided through a shielded cable with a connector that mates the module to the power supply. A multiple receiver version with individual control over each is available.

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Series F Amplified Dual Differential Photodetector Modules Summary and Prices

Input Optical Connector: none 2.5mm ceramic ferrule NTT-FC SC ST SMA other_______________ Polish: flat PC SPC APC(8 degrees) other _____________________ Optical Cable: 9/125microm 50/125microm 62.5/125micro other___________________ Jacket: 0.9mm buffer only 3mm Kevlar and Polymer over 0.9mm buffer ______________ Length: 1 meter (standard) other_________________ Light-Collection Optics (Pair): none 6mm fixed aspheric ($450) alignable Micro-Rail and "C" thread compatible ($790) Large Aperture (inquire) Matched Pair of Photodiodes: GaAs, 450-870nm, 10 GHz ($2190) InGaAs-1, 850-1700nm, 3.5 GHz ($1590) InGaAs-2, 850-1700nm,7.5 GHz ($1990) InGaAs-3, 650-1650nm,>10 GHz ($2190)

Amplifier and Coupling Options: True DC Coupling, DC with Offset Null Mod 1D, 10GHz ($575) Mod 2D, 7GHz ($575) Mod 4D, 2.8GHz, 2,500 ohms ($575) AC Coupling Only Mod 1A, 10GHz ($275) Mod 2A, 7GHz ($275) Mod 4A, 2.8GHz, 2,500 ohms ($275) Mod 11A, 7GHz ($450) Mod 22A, 5GHz ($450) Mod 42A, 2.8GHz, 7,500 ohms($450) Mod 44A, 2.8GHz, 60,000 ohms($450) Mod 111A, 3,200 ohms ($625) Mod 222A, 10,800 ohms ($625) Mod 422A, 45,000 ohms ($625) Mod 442A, 200,000 ohms ($625) Mod 444A, 1.6 x 106 ohms ($625) Output Electronic Connector: SMA other________ Gender: male plug (as shown) female jack Packaging: Free-standing ,with power cable PC Board Mount,with solder lugs for power External Power Supply: (shipped as a separate item) 12volt rechargeable gel-cell with EMI/RFI shielding ($275) Multiple Output version, powers up to 4 modules (please inquire)

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

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How to Order

We will build your Dual Differential Photodetector Module to your specifications. The price of your detector is simply the addition of the prices of specified options with cost amounts listed. 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.

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

tel: (+1) 925 989 4930
fax: (+1) 925 449 4647
email: sales@mfaoptics.com

 

  ©1999-2010

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email: sales@mfaoptics.com

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