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Systems

Welcome to the online documentation of our systems. Bridge12 will no longer distribute paper manuals to ensure our documentation is always up to date. If you have questions, or suggestions for edits please contact us at info@bridge12.com.

Important

Please read the documentation for you product carefully to avoid any damages to the Bridge12 system.

1 - X-Band IF

Bridge12 X-Band IF System for Pulse EPR Spectroscopy

The Bridge12 X-Band IF system is at the heart of all Bridge12 EPR spectrometers. The system is highly modular. For X-Band EPR spectroscopy only a high-power microwave amplifier, digitizer and AWG is required.

The system can be completely controlled using SpecMan4EPR.

1.1 - X-Band IF Backpanel Connections

Backpanel connections of the X-Band IF system.

Below, please find a list and description of the backpanel connectors of the X-Band IF system. Please refer to the figure below for the location of connections.

Warning

Whether a connector is used for an input or output signal is labeled in the table below. Please make sure the user makes the correct connections. Wrong connections can lead to permanent damages of the system.

RF Connections

Please refer to the table below for a description of the back panel connectors of the X-Band IF system. The function (I/O - input/output) of the connector is indicated in the second column.

Information

Make sure all connections to the back panel connectors are properly tighten. SMA connections should be tightened using a torque wrench (recommended torque 10 Nm).

Side Panel

Connector I/O Type Description
SIG I SMA Input signal for the receiver.
LO2 O SMA LO2 output of the microwave synthesizer (channel B)

Receiver (RCVR)

Connector I/O Type Description
RCVR I O SMA I channel of the quadrature receiver channel. This is typically referred to as the real signal of the detected EPR signal.
RCVR Q O SMA Q channel of the quadrature receiver channel. This is typically referred to as the imaginary signal of the detected EPR signal.
RCVR IF I SMA IF input of the RCVR. For X-Band operation, this should be connected to the LO1 output of the microwave synthesizer (channel A). Suggested Cable

Pulse Forming Unit (PFU) and AWG Input

Connector I/O Type Description
PFU TX O SMA Output of the PFU. This signal is typically routed to the high-power amplifier or the active multiplier chain (AMC) in high-field/high-frequency EPR spectrometers.
PFU BLNK I SMA Blanking gate of the PFU. TTL logic. Active high. This signal has to be connected to the pulse programmer.
AWG I I SMA I channel input of the PFU. This signal needs to be connected to the output channel of the AWG.
AWG Q I SMA Q Channel input of the PFU. This signal needs to be connected to the output channel of the AWG.
AWG AUX I SMA Auxillary input of the IQ mixer LO channel.

Synthesizer and Monitors

Connector I/O Type Description
AUX IN I SMA Auxillary microwave signal input. This signal is combined with the microwave signal generated by the IQ mixer of the PFU and allows the user to inject an additional, user-created microwave signal.
AUX OUT O SMA LO signal of the LO input for the IQ mixer of the PFU. This signal is similar to LO1.
LO1 O SMA LO1 signal of the X-Band IF system (channel A of the synthesizer).
LO2 O SMA LO2 signal of the X-Band IF system (channel B of the synthesizer).
RCVR O SMA Receiver input monitor.
PFU O SMA PFU output monitor.

Reference Clock and External IO

Connector I/O Type Description
10 MHZ O SMA Oven-controlled 10 MHz reference clock signal. Output power level 10 dBm.
VCA O SMA 0 - 5 V DC signal. The output level of this signal can be controlled through the software. This signal is typically used for the Voltage Controlled Attenuator (VCA) of a high-frequency AMC.
EXT O D-Sub 9 pin d-sub connector. Pin Out
IO O D-Sub 9 pin d-sub connector. Pin Out

Other Connections

Side Panel

Connector I/O Type Description
12 V O LEMO 12 V output. This supply voltage can be used to power up external equipment. Do not exceed 200 mA. Mating Connector

Other Connectors

Connector I/O Type Description
EXT PWR O M12 Power supply e.g. for a frequency extension. Available voltages: -12 V, -5 V, 5 V, 12 V, 15 V
PWR I Amphenol Power inlet for the X-Band IF system. Please only use the power supply supplied with the system to avoid permanent damages.
PLS I/O USB USB connection from the X-Band IF to the pulse programmer. This USB port is connected to the internal USB hub of the X-Band IF system.
PC I/O USB USB connection to remote PC.
GND n/a STUD A ground (GND) post is located in the lower left corner of the back panel.

Warning

Only use the power adapter that came with the X-Band IF system to power up the instrument.

Failure to use the correct power adapter can lead to permanent damage of the system.

If you are unsure about the power adapter, please contact Bridge12 at support@bridge12.com

1.2 - Digital Demodulation

How to use digital demodulation with the X-Band IF system.

The Bridge12 X-Band IF system supports digitial demodulation. Digital demodulation allows for easy removal of baseline artifacts and will result in a much cleaner signal detection. Instead of down-converting the EPR signal to DC level, the LO frequency is slightly offset and the signal is detected at a frequency of e.g. 200 MHz. The exact frequency depends on the sampling rate and input bandwidth of the digitizer (or oscilloscope).

Information

Digital demodulation is highly recommended for the X-Band IF system. Even an offset of just 20 MHz will greatly remove many artifacts from the baseline.

The example below shows a digitally demodulated signal of a 2-pulse Hahn echo of a sample of BDPA in polystyrene, recorded at Q-band frequencies.

We recommend using an intermediate frequency of about half the bandwidth of the digitizer. For example, if the digitizer has an input bandwidth of 400 MHz, we recommend to choose an intermediate frequency of 200 MHz.

To acquire the EPR signal at a This offset can be achieved in two ways:

1. Offsetting the AWG Frequency

The simplest way to use digital demodulation is by offsetting the frequency for the AWG generated microwave pulses. Instead of generating a rectangular pulse at DC level, the user can create a pulse at a frequency of e.g. 200 MHz. To make sure the frequency of the microwave pulse is within the bandwidth of the resonator, the microwave frequency needs to be lowered by the same amount. For example, to generate a microwave pulse at 9.8 GHz with an offset of 200 MHz:

  1. Set the LO1 frequency of the synthesizer to 9.6 GHz (9.8 GHz - 0.2 GHz)
  2. Set the AWG frequency to 200 MHz
  3. Set the demodulation frequency in SpecMan to -200 MHz.

2. Offsetting the Receiver Frequency

If pulses are not created by an AWG but for example by a pulse generator, digital demodulation can still be used. However, in this case, both microwave synthesizers, LO1 and LO2, have to be utilized.

To use digital demodulation with DC pulses follow these steps:

  1. Connect the RCVR IF to the LO2 output.
  2. Set the LO1 frequency on-resonant with the resonator frequency, e.g. 9.6 GHz.
  3. Set the LO2 frequency to 9.4 GHz. That way the echo signal has to be demodulated using a frequency of 200 MHz (9.6 GHz - 9.4 GHz = 0.2 GHz).

Demodulating the Signal (Demodulating the Signal)

Once the signal is digitized it has to be digitally demodulated.

In SpecMan4EPR

Demodulating the EPR signal in SpecMan4EPR is very straight forward and simple. Simply make sure the Demodulation Frequency is set to the correct value and the spectrum is automatically demodulated when the data is acquired.

Manually

If the X-Band IF is used manually, demodulation must be performed by the user during post-processing of the EPR data. This can be conveniently done by using the demodulate function in DNPLab.

DC Detection

To down-convert the EPR signal to DC level, connect the LO1 output of the synhesizer to the IF input of the receiver and make sure the frequency offset for the AWG pulses is set to 0 MHz.

1.3 - Example Configurations

Example configurations for different frequency bands.

The Bridge12 X-Band IF system can be used to operate EPR spectrometers from S-Band (2 GHz) to the millimeter regime (> 400 GHz).

Below, please find example configuration for different operating frequencies.

1.3.1 - Example: Pulsed X-Band Operation

Example configuration for pulsed X-Band EPR spectroscopy.

A typical configuration of the X-Band IF system for pulsed X-Band spectroscopy is shown in the figure below. Connections that are not required are greyed out.

Connector Description
RCVR IF
to LO1
Connect a microwave cable between the LO1 synthesizer output and the RCVR IF input. This has to be a microwave cable, able to carry frequencies up to 10 GHz (Suggested Cable). This is the default configuration when using digital demodulation and offsetting the pulse frequency using the AWG.
RCVR I
RCVR Q
Connect the RCVR I and RCVR Q channel to the digitizer or oscilloscope. The EPR signal will appear here.
AWG I
AWG Q
Connect the AWG I and AWG Q connectors to the arbitrary waveform generator. Alternatively, these channels can also be connected directly to the output of a pulse programmer to generate rectangular pulses at the LO1 frequency. If you have questions about these mode, please contact Bridge12 at support@bridge12.com.
PFU TX This is the output of the X-Band IF system. Connect this connector to the input of the high-power pulse amplifier. Depending on the type of the amplifier an additional pulse blanking gate is required as a channel of the pulse programmer.
PFU
BLNK
Blanking gate of the PFU. This is not the amplifier blanking gate. This gate is active high and needs to be high to be able to transmit microwave pulses.
10 MHz
CLK
Connect the system clock to each, the digitizer and the AWG. That way, the X-Band IF system provides the master clock to synchronize all other instruments. The X-Band IF master clock runs at 10 MHz. In cases when the AWG clock is higher, the user may want to synchronize the system to the AWG clock to minimize pulse jitter.

1.4 - Manual Operation of the X-Band IF

Required software to install to manually operate the X-Band IF system.

To manually operate the X-Band IF system please install the following software:

Once these two software packages are installed, the X-Band IF system can be completely remote controlled.

1.4.1 - Controlling the X-Band IF Synthesizer

How to control the X-Band IF microwave synthesizer manually

Please make sure the control software for the synthesizer is installed. If you haven’t done so, you can download it here.

1.4.2 - DAQ Control

How to control the analog and digital lines of the X-Band IF system manually.

Please make sure the control software for the DAQ interface is installed. If you haven’t done so, you can download it here.

Connecting to the DAQ Interface

To connect to the DAQ interface follow these steps:

  1. Make sure the X-Band IF USB interface is connected to the host computer.
  2. Start Kipling
  3. In the GUI click the green USB button (see figure above, left). The USB button will turn red, indicating that Kipling is connected to the DAQ interface (see figure above, right).

Digital Input/Output Control

To control the digital input/output lines click on the menu item Dashboard (see figure above). Each of the lines can be configured as an input or output by selecting the control from the drop-down menu. If the line is configured as an input the indicator to the left will show whether the line is logic high or low. If the line is configured as an output, the status can be changed by selecting the desired status from the drop-down menu.

Below is a list of the different digital channels used by the X-Band IF system.

Pulse Forming Unit (PFU)

Bit Name Function
CIO0 AWG LO select for PFU. 0 - Internal synthesizer (LO1), 1 - AUX LO, auxillary LO input on back panel

Receiver (RCVR)

Bit Name Function
CIO1 Enable/Disable video amplifiers. 0 - disabled, 1 - enabled
FIO4 Microwave signal amplifier, 0 - disabled, 1 - enabled +20 dB gain

Analog Output Control

The value of the varios analog outputs can be controlled from the Register Matrix panel. The values for TDAC0 - TDAC3 can be set between -10 and +10 V, with a resolution of 16 bit.

Below is a list of the different analog channels used by the X-Band IF system.

Receiver

Bit Name Function
TDAC0 Video amplifier gain control (I channel), value from -10 to 10 V, -10 V - 30 dB gain, 10 V - 65 dB gain
TDAC1 Video amplifier gain control (Q channel), value from -10 to 10 V, -10 V - 30 dB gain, 10 V - 65 dB gain
TDAC2 LO level receiver, value from -10 to 10 V, -10 V - 0 attenuation, full power on LO of IQ mixer (RCVR), 10 V - 30 dB attenuation, lowest power on LO of IQ mixer (RCVR)

Miscellaneous Other Controls

The X-Band IF system has several spare digital and analog input and output lines. These lines can be configured by the user.

Back Panel EXT Connector (9 pin sub-D)

Bit Name Pin Number
sub-D
Function
EIO0 1 DAQ bit EIO0, can be configured as input and output, TTL level
EIO2 2 DAQ bit EIO2, can be configured as input and output, TTL level
EIO4 3 DAQ bit EIO4, can be configured as input and output, TTL level
EIO6 4 DAQ bit EIO6, can be configured as input and output, TTL level
GND 5 Systems GND
EIO1 6 DAQ bit EIO1, can be configured as input and output, TTL level
EIO3 7 DAQ bit EIO3, can be configured as input and output, TTL level
EIO5 8 DAQ bit EIO5, can be configured as input and output, TTL level
EIO7 9 DAQ bit EIO7, can be configured as input and output, TTL level

Back Panel DIO Connector (9 pin sub-D)

Bit Name Pin Number
sub-D
Function
MIO0 1 DAQ bit MIO 0, can be configured as input and output (TTL level)
MIO2 2 DAQ bit MIO 2, can be configured as input and output (TTL level)
DAC1 3 DAQ bit DAC 1. This is an analog output. The value can be changed between 0 and 5 V. The output is controlled from the Dashboard menu
AIN1 4 DAQ bit EIO 6, can be configured as input and output (TTL level)
GND 5 Systems GND
MIO1 6 DAQ bit MIO 1, can be configured as input and output (TTL level)
IO4 7 TDAC 3, values (set in software) -10 to 10 V, output 0 to 10 V
AIN0 8 DAQ bit EIO 5, can be configured as input and output (TTL level)
VS 9 5 V supply voltage

Back Panel VCA Connector (SMA)

Bit Name Function
DAC0 VCA control (back panel). This is an analog output. The value can be changed between 0 and 5 V. The output is controlled from the Dashboard menu, value 0 to 5 V

2 - Quasi-Optics

Quasi optical (QO) systems are used in high-field EPR and DNP systems to control the microwave beam propagation. For example, to separate the incident microwave beam from the reflected beam in a reflection-type EPR bridge. QO is a highly versatile technology to build attenuators, universal polarizers, and beam splitter. If you would like to learn more about it check out our page on Quasi-Optics (QO).

Here you will find the online documentation for some of our QO components. Many QO systems are customer specific. If you have questions about your individual system please contact Bridge12 at support@bridge12.com.

2.1 - Polarizing Transforming Reflector (PTR)

The Bridge12 Polarization Transforming Reflector (PTR) is a universal polarizer. The PTR can convert a linearly polarized microwave beam into a circularly polarized beam, or rotate the E-field vector by any angle.

Bridge12 Polratization Transforming Reflector (PTR)

Bridge12 Polratization Transforming Reflector (PTR)

This is the online documentation of the PTR. For product related information check out the Bridge12 PTR Product Page. The theory and operation of the PTR has been published in:

  • Chen, Jeson, and Thorsten Maly. “Compact, Tunable Polarization Transforming Reflector for Quasi-Optical Devices Used in Terahertz Science.” Review of Scientific Instruments 93, no. 1 (January 1, 2022): 013102. https://doi.org/10.1063/5.0036292.

If you are using a Bridge12 PTR in your research please consider citing the device in your publication.

2.1.1 - Theory of Operation

The PTR was first described in the literature by Howard et al. operating at a frequency of 28 GHz. Despite its low insertion loss, the PTR has only been used in QO systens for high-field EPR/DNP spectroscopy in some rare instances.

Theory

Wire Grids

Before discussing the PTR in more detail, we will briefly review some fundamental properties of wire grid polarizers.

Free-standing wire grid polarizers made from cylindrical metallic wires either transmit or reflect electromagnetic radiation depending on the orientation (polarization) of the incident E field vector with respect to the grid wire orientation. For cylindrical wires with wire radius \(d\) and wire separation distance \(S\) with \(d \ll S\), the frequency dependent transmission coefficient for an electric field vector oriented parallel to the wire grid can be calculated using the Jones Matrix formalism. The corresponding reflection and transmission matrices are:

$$ C_{R} = \begin{pmatrix} -\cos^{2}{\theta} & -\cos{\theta} \sin{\theta} \\ \cos{\theta} \sin{\theta} & \sin^{2}{\theta} \end{pmatrix} $$

and

$$ C_{T} = \begin{pmatrix} \sin^{2}{\theta} & -\cos{\theta} \sin{\theta} \\ -\cos{\theta} \sin{\theta} & \cos^{2}{\theta} \end{pmatrix}. $$

This only correct if the grid orientation to be perpendicular to the propagation direction of the beam (\(\theta^{ \prime} = 0^{\circ}\)). However, if the purpose of the grid is to clean up the polarization of the microwave beam, the resulting reflected microwave power should be directed away form the source and not directly reflected back. This can be achieved by orienting the grid at an angle of \(\theta^{\prime} = 45^{\circ}\). In this case determining the reflection and transmission coefficients is less intuitive. This is summarized in the following figure (Figure 1).

Figure 1: Grid orientation for partial beam reflection/transmission

Figure 1: Grid orientation for partial beam reflection/transmission

If the grid is oriented perpendicular to the beam propagation direction (\(\theta^{ \prime} = 0^{\circ}\)) the free-standing wire grid needs to be rotated by (\(\theta = 45^{\circ}\)) to transmit 50 % of the power (see Figure 1A). On the other hand, if the grid is oriented at an angle (\(\theta^{ \prime} = 45^{\circ}\)) the wire grid needs to be rotated by (\(\theta = 54.7^{\circ}\)) to transmit 50 % of the power and reflect 50 % of the power (see Figure 1B). For more details check out Paul Goldsmith’s book Quasioptical Systems: Gaussian Beam Quasioptical Propagation and Applications (chapter 8.6.2, page 210).

Figure 2: The free-standing wire grid as a beam splitter

Figure 2: The free-standing wire grid as a beam splitter

The power transmission and reflection for a variable grid is shown in Figure 2. By rotating the grid and varying the angle \(\theta\) from 0º to 90º the beam can be continuously attenuated. Depending on the quality of the grid this attenuation can reach values of - 30 dB or lower.

Polarization Transforming Reflector (PTR)

The PTR consists of two principle components: 1) A free-standing wire grid and 2) A flat metal reflector. The free-standing wire grid is made from metallic wires having a diameter of d and separated by a distance of S (see figure below). Directly located behind the grid is a flat mirror. A schematic of the PTR is shown in Figure 2 (left).

Figure 2: Bridge12 Polarization Transforming Reflector (PTR). Left: Schematic of the PTR. Right: Dependance of the output polarization from the mirror/grid separation distance. Ev - vertically polarized e-field, Eh - horizontally polarized e-field, Er - right hand circularly polarized e-field, El - left hand circularly polarized e-field.

Figure 2: Bridge12 Polarization Transforming Reflector (PTR). Left: Schematic of the PTR. Right: Dependance of the output polarization from the mirror/grid separation distance. Ev - vertically polarized e-field, Eh - horizontally polarized e-field, Er - right hand circularly polarized e-field, El - left hand circularly polarized e-field.

By changing t, the distance between the flat mirror and the wire grid polarizer of the PTR it is possible to change the polarization state of e.g. a linearly polarized Gaussian incident beam to from linear to circular clockwise and counter-clockwise polarization (Figure 2, right).

How it works

Assuming the gird/mirror pair of the PTR is oriented at angle \(\theta = 45^{\circ}\) with respect to the propagation direction of the incident beam and a grid wire orientation of (\(\theta^{ \prime} = 54.7^{\circ}\)) half of the power of the incident beam will be reflected by the wire grid at point A (see Figure 2, left). The remaining portion of the beam will travel through the grid and be reflected by the flat mirror surface at point B (see Figure 2, left).

Depending upon the distance t between the wire grid and the flat mirror surface, the portion of the beam transmitted by the wire grid will have to travel an additional distance ABC (see Figure 2, left) and will accumulate a phase difference \(\rho\) with respect to the portion of the beam taht is reflected by the wire grid at point A (see Figure 2, left).

For the incoming beam, having a wavelength of \(\lambda \), propagating at an incident angle \(\theta = 45^{\circ}\) and a grid–mirror separation of t, the optical path difference P to travel the additional distance is:

$$ P = AB + BC \\ P = 2t \cos(\theta^{\prime}). $$

The phase difference \(\rho\) between orthogonal components is given by

$$ \rho = 4 \pi t \cos(\theta^{\prime} \lambda), $$

and the separation distance between orthogonal components \(\Delta\) (beam walk-off, Figure 2 right) is given by

$$ \Delta = 2t \sin(\theta^{\prime}). $$

By changing the distance t, it is possible to change the phase difference between the two beam components and therefore to change the polarization of the e-field of the reflected beam, e.g., from linear to circular or arbitrary linear polarization orthogonal to the propagation axis, with respect to the reflected beam. Choosing the correct distance t, an incident linearly polarized THz beam can therefore be transformed into a beam with a phase difference given by \(\rho\) with respect to the orthogonal polarization. This property enables transformation of, e.g., linear polarization to circular polarization, similar to a quarter-lambda waveplate.

2.1.2 - Installation

The PTR is compatible with the Bridge12 bread-board for quasi-optical instrumentation. The bread-board is based on a 2.5 in. by 2.5 in. grid. It is commonly referred to as a 1 1/2 - 3 - 1 1/2 optic. This means, make sure that there are 2 empty cube positions between two refocusing mirrors.

Installation

To install the PTR:

  1. Slide the dowel pin into the clearance hole of the bread board
  2. Orient the PTR
  3. Lock the PTR position by fastening the 1/2-40 socket head screw

Optimizing the Position

The PTR, as all Bridge12 QO elements only have one degree of freedom (rotation about the dowl pin) to optimize the insertion loss or overall transmission loss of a QO system. To minimize transmission losses:

  1. Loosen the 1/4-20 socket head screw. Do not remove the screw from the bread board
  2. Monitor the transmitted power
  3. Rotate the PTR while maximizing the transmitted power

Note

QO systems can have many individual configurations. In some systems it is easier to monitor the transmitted power, in others it is more convenient to monitor the reflected power. If you are not sure how to optimize the transmission losses in your QO system please contact Bridge12 Technologies, Inc. at support@bridge12.com.

Warning

Do not touch the free-standing wire grid of the PTR. The grid is located at the front of the PTR. The grid is extremely fragile and can be easily destroyed by sharp objects (e.g. screw drivers).

Adapters

The PTR is fully compatible with the Bridge12 QO bread board design. Bridge12 offers adapter plates if you are using a different bread board design. Please contact us at info@bridge12.com for more information.

2.1.3 - Maintenance

The Bridge12 PTR is completely maintenance free. If you experience any problems please contact Bridge12 at support@bridge12.com.

Warning

The free-standing wire grid of the PTR is extremly fragile. Do not use any sharp tools (e.g. blades, screw drivers, etc.) when working around the PTR.

2.1.4 - References

The PTR is not a new device and has been described throughout the scientific literature. Some major references are:

  • Howard, J., W. A. Peebles, and N. C. Luhmann. “The Use of Polarization Transforming Reflectors for Far-Infrared and Millimeter Waves.” International Journal of Infrared and Millimeter Waves 7 (October 1, 1986): 1591–1603. https://doi.org/10.1007/bf01010760.
  • Earle, Keith A., Dmitriy S. Tipikin, and Jack H. Freed. “Far-Infrared Electron-Paramagnetic-Resonance Spectrometer Utilizing a Quasioptical Reflection Bridge.” Review of Scientific Instruments 67 (1996): 2502–13.
  • Amer, N., W. C. Hurlbut, B. J. Norton, Yun-Shik Lee, and T. B. Norris. “Generation of Terahertz Pulses with Arbitrary Elliptical Polarization.” Applied Physics Letters 87, no. 22 (November 28, 2005): 221111. https://doi.org/10.1063/1.2138351.
  • Chuss, David T., Edward J. Wollack, Ross Henry, Howard Hui, Aaron J. Juarez, Megan Krejny, S. Harvey Moseley, and Giles Novak. “Properties of a Variable-Delay Polarization Modulator.” Applied Optics 51, no. 2 (January 10, 2012): 197. https://doi.org/10.1364/AO.51.000197.

However, when characterizing the PTR developed by Bridge12 Technologies, Inc. we realized that the PTR can also be used as an Universal Polarizer. This properties hasn’t been reported before and was first described in:

  • Chen, Jeson, and Thorsten Maly. “Compact, Tunable Polarization Transforming Reflector for Quasi-Optical Devices Used in Terahertz Science.” Review of Scientific Instruments 93, no. 1 (January 1, 2022): 013102. https://doi.org/10.1063/5.0036292.

If you are using a PTR manufactured by Bridge12, please consider referencing the above publication.

Initial results were presented at the 2018 ENC Conference as a poster contribution by Jeson Chen.

Poster by Jeson Chen and Thorsten Maly, presented at the 2018 ENC

Poster by Jeson Chen and Thorsten Maly, presented at the 2018 ENC