Ultrafast Fiber Optic Photodetectors

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While each DXM Series model is designed and intended for operation over the specified wavelength range, each will respond, with reduced performance, to optical input at shorter wavelengths, as shown by the shaded regions. See the Responsivity plots in the Specs tab for details. Please contact Tech Support for more information.

Janis Valdmanis, Ph.D. Optics
Ultrafast Optoelectronics
General Manager

We Design, Develop, and Manufacture
Equipment up to 70 GHz

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Features

• Visible, Near-Infrared, or Broadband Wavelength Ranges
• DC-Coupled Output
• Hermetically Sealed GaAs or InGaAs Detector Module
• Internal SMF-28 Single Mode Fiber: DXM12CF, DXM25CF, DXM30AF, and DXM20AF
• Internal OM4 Multimode Fiber: DXM12DF, DXM25DF, and DXM30BF
• RF Output Signal via 2.92 mm (K™)^† Connector
• Built-In DC Photocurrent Monitor
• Digital Output Sent to Display
• Analog Output via SMA Connector
• Replacement Power Supply Available

The DXM series of Ultrafast Detectors include single-mode and multimode fiber-coupled photodetectors with wide wavelength ranges, as shown to the right. Each provides a high-fidelity electrical output pulse in response to an optical input pulse, and their clean impulse responses have full width half maxima (FWHM) down to 15 ps. The core element of each detector is the fiber-coupled, hermetically sealed microwave detector module. For convenience and simplicity of use, the module is mounted inside a rugged aluminum housing that includes a rechargeable battery with 500 mAh capacity, current monitor circuitry, and a digital display of the DC photocurrent.

Our single mode detectors contain 9 µm core SMF-28 single mode fiber, while our multimode detectors contain 50 µm core OM4 multimode fiber. Optical input can be coupled from an FC/PC-terminated fiber via the FC bulkhead connector. Our multimode ultrafast detectors are designed to accept input from multimode or single-mode optical fiber connectors, making them a versatile measurement instrument for research and commercial applications. We offer single mode and multimode hybrid patch cables to facilitate connecting optical cables with different connector types. RF signal output is available via a female 2.92 mm RF connector, which may be connected to a measurement instrument using suitable microwave cables or adapters. Measurements of the DC photocurrent can be viewed using the digital display, and an SMA jack on the input panel provides the analog current monitor output signal. Please see the Operation tab for additional information on functionality and operation.

Included with each DXM series detector head is a power adapter with a mini-B USB plug for charging the battery and a mounting bracket (ECM100, also available below) that snaps onto the side of the housing. The ECM100 bracket has a #8 (M4) counterbore, which allows easy mounting to a post or any other component with an 8-32 (M4) threaded hole.

The performance of each DXM series ultrafast detector is factory tested, and the individualized test results are provided with the detector. Please contact Tech Support if you would also like to receive a data file containing these test results. A sample data sheet for the DXM20AF ultrafast detector can be viewed here.

^†K™ is a trademark of Anritsu.

All specifications for the DXM12 and DXM25 series are typical for 850 nm and 25 °C operation, unless otherwise noted. 
All specifications for the DXM30 series and the DXM20AF are typical for 1550 nm and 25 °C operation, unless otherwise noted.

Parameter		DXM12CF	DXM12DF	DXM25CF	DXM25DF	DXM30AF	DXM30BF	DXM20AF
Operation
Wavelength Rangea		Visible				Broadband		Near Infrared
		700 nm - 870 nm				750 nm - 1650 nm		1250 nm - 1650 nm
Frequency Responseb		DC - 12 GHz		DC - 25 GHz		DC - 30 GHz		DC - 20 GHz
Internal Fiber Type (Core Diameter)		SMF-28 (9 µm)	OM4 (50 µm)	SMF-28 (9 µm)	OM4 (50 µm)	SMF-28 (9 µm)	OM4 (50 µm)	SMF-28 (9 µm)
Impulse Response (FWHM)b		29 ps		19 ps		15 ps		18 ps
Conversion Gain (Into External 50 Ω Load)		15 V/W	14 V/W	12.5 V/W	11 V/W	19 V/W	16.5 V/W	22.5 V/W
Photodiode Material		GaAs				InGaAs
Responsivity (At the FC/PC Connector)	Single Mode Input	0.6 A/W		0.5 A/W		0.5 A/W (850 nm) 0.8 A/W (1310 nm) 0.7 A/W (1550 nm)		0.9 A/W (1310 nm) 0.9 A/W (1550 nm)
	Multimode Input	-	0.55 A/W	-	0.45 A/W	-	0.45 A/W (850 nm) 0.7 A/W (1310 nm) 0.6 A/W (1550 nm)	-
Optical Return Loss	Single Mode Input	-30 dB	-25 dB	-30 dB	-25 dB	-25 dB (850 nm) -25 dB (1310 nm) -20 dB (1550 nm)	-15 dB (850 nm) -15 dB (1310 nm) -15 dB (1550 nm)	-25 dB (1310 nm) -30 dB (1550 nm)
	Multimode Input	-	-18 dB	-	-18 dB	-	-10 dB (850 nm) -10 dB (1310 nm) -10 dB (1550 nm)	-
Peak Optical Input Power (Max)c		75 mW		100 mW		50 mW		50 mW
Noise Equivalent Power (NEP)d		43 pW/Hz1/2	47 pW/Hz1/2	51 pW/Hz1/2	57 pW/Hz1/2	34 pW/Hz1/2	40 pW/Hz1/2	28 pW/Hz1/2
Dark Current (Max)		50 nA
Average Optical Input Power (Abs. Max)c		+10 dBm (10 mW)
RF Output Voltage (Max)e		1 V
Reverse Termination Impedance (RF Output)		50 Ω
Click the Icons to View Data Graphs		Typical Graphs		Typical Graphs		Typical Graphs		Typical Graphs

• While each DXM series model is designed and intended for operation over the specified wavelength range, each will respond, with reduced performance, to optical input at shorter wavelengths. For example, representative values for the DXM20AF at 780 nm are: responsivity of 0.25 A/W, impulse response of 23 ps, and bandwidth of DC - 12 GHz.
• Typical Values at 780 nm for the DXM12CF, DXM12DF, DXM25CF, and DXM25DF, and at 1560 nm for the DXM20AF, DXM30AF, and DXM30BF.
• Both average and peak optical input power specifications must be met to avoid damaging the device. The average is specified over any 1 s time period.
• The NEP is limited by the thermal noise of the 50 Ω internal and external load resistors.
• Into External 50 Ω Load

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The front panel of every DXM Series Ultrafast Detector includes engravings giving the wavelength and frequency response ranges. The button toggles the DC photocurrent monitor display between units of mA and µA. For more details on the operation of these detectors, see the Operation tab.

Quick Start Guide

ESD Sensitive Components: Please note that the components inside the DXM series units are ESD sensitive. Take all appropriate precautions to discharge personnel and equipment before making any electrical connections to the unit. This especially applies to coaxial connecting cables that can accumulate capacitive charge.

Charging the Detector: The detector arrives with the battery partially charged. The battery can be fully charged using the included charger and USB adapter cable connected to the USB charger jack indicated in Figure 1. The yellow indicator LED, which is also located on the input panel, illuminates to confirm it is charging properly, and the green LED next to it illuminates when the unit is fully charged. The battery may also be charged using USB chargers for phones, tablets, or similar products. These will charge the battery at a maximum rate of 500 mA. Non-dedicated charging USB ports (e.g. those on a PC) will charge at a lower 100 mA rate.

Mounting the Detector: The included ECM100 mounting clamp, also available below, has a single counterbore that accepts a 8-32 (M4) cap screw (not included). Screw the clamp to the desired base or post before snapping it to the side of the detector housing and securing it using the integrated 5/64" (2 mm) locking screw. 

RF and Photocurrent Monitor Output: Connection cables attached to the RF output port, shown in Figure 3, and SMA photocurrent monitor port, shown in Figure 1, must be properly shielded. Attach the RF output of the DXM series unit to the measurement instrument using suitable cables or adapters, such at Thorlabs' microwave cables and adapters. The measurement instrument must have a 50 Ω input and adequate bandwidth to resolve the high-speed signal from the DXM series ultrafast detector. 

Optical Fiber Input: Ensure the input optical power does not exceed +10 dBm. The FC/PC bulkhead connector used to couple the optical input signal to the detector is located on the input panel of the unit, shown in Figure 1. Fiber connector tips should be cleaned properly before making any connections. While multimode versions of the DXM series may use either single mode or multimode fiber inputs, single mode versions require 9 µm core single mode fiber.

DC Photocurrent Monitor: The DC photocurrent can be monitored directly by viewing the built-in digital display shown in Figure 2, as well as by using most voltmeters to read the analog voltage signal output via the high-impedance SMA jack located on the input panel shown in Figure 1. The units on the displayed digital current measurement can be toggled between µA and mA using the button on the front panel. There may be a small discrepancy (within specification) between the screen and SMA monitor output signal. The digital display reports a wide range of current values, up to 20 mA with a resolution of 1 nA, with the display automatically changing range in response to the signal magnitude. The analog voltage signal sent to the SMA connector has a linear relationship with the measured DC photocurrent up to 3.5 V: the transimpedance gain of the current monitor provides 200 mV per 1 mA of photocurrent. This linear relationship limits the current range reported by the analog SMA output signal, so that the range is smaller than that provided by the digital display. 

Cleaning the Housing: Use a soft cloth moistened with mild glass cleaner. Do not spray directly onto unit.

Housing Features

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Figure 3: Output Panel of the DXM Series Ultrafast Detectors

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Figure 2: Front Panel of the DXM25CF 25 GHz Detector

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Figure 1: Input Panel of the DXM Series Ultrafast Detectors

Components Included with the DXM Series Ultrafast Detectors

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Components of the DXM Series Ultrafast Detectors
(DXM12CF Detector Head Shown)