Product Info.



Here is the summary of the frequently asked questions and the answers.

Frequently asked questions Answers
E/O and O/E converters

How come the frequency modulated electromagnetic wave can be transmitted as optical signal ?
Graviton's O/E and E/O converter products are the devices which convert between intensity changes of optical signal to voltages of electrical signal and vice versa.
By E/O converters, voltage of frequency modulated electrical input signal(V) is converted to optical power(W).
The frequency of optical signal does not depend on the voltage of the frequency modulated electrical signal, but the characteristics of the optical element implemented to the E/O converter.
For example, in case the frequency of the modulated electrical signal is 100MHz, the frequency of the output optical power signal will be 100MHz. The frequency of the optical signal is not changed By O/E converters, optical power(W) is converted to voltage of output electrical signal(V). When converting the optical power signal to the voltage of the electrical signal, the frequency of the optical intensity signal is simply detected, and no special operation is carried out on the voltage of the output signal. The frequency of optical signal is 100MHz, the output voltage of electrical signal will be 100MHz.
However, some effect on the output voltage of the electrical signal could be considered as the conversion sensibility of the photodetector depends on the variation of the optical frequency (wavelength of optical signal).
Please tell me about the conversion carried out between the intensity change of optical signal and the voltage of electrical signal ? The numbers of cycle of electric signal are converted to those of optical intensity and vice versa. The frequency of electrical signal input to E/O converter is converted to the cycle of optical intensity, and the cycle of the optical intensity is converted to the frequency of the original electrical signal by O/E converter.
Regarding the power supply Is the power supply AC adapter or Battery ? Power supply
In Graviton's O/E converters including SPD-1 and LPD-1 require both of negative and positive power supplies of ±15V.
The positive current is about 100mA and the negative current is about 20mA. Only SPA-2 requires single power supply of +12V to +18V.
Graviton's O/E converter comes with a dedicated power cord attached with LEMO connectors on both ends and an auxiliary power cord attached with a LEMO receptacle and three AWG26 wires.
In general, an oscilloscope or a spectrum analyzer has the power output terminal for the probe, the power can be supplied from such a unit to Graviton product by using the dedicated power supply cord comes with.
In case that an electric measuring instrument which is used along with Graviton’s product does not have a compatible power output terminal for the probe, you need regulated power supplies of positive and negative.
You can connect the power supplies to Graviton’s product by using the dedicated power supply cord and the auxiliary power supply cord.
Does sampling by DC to 1.5GHz means 3GHz in 1/0 ?
About sampling frequency
Sampling frequency in a range from DC up to 1.5GHz does not mean 3GHz in 1/0.
LPD-1 converts the intensity modulated waveform of input optical signal to the voltage waveform of output electrical signal in analog.
Any operation such as binarization by a comparator is not executed inside of LPD-1. Analog frequency bandwidth is from DC to 1.5GHz. In case observing the light modulated in digital, up to 2Gbps is appropriate bit rate. If 3 Gbps light is input, eye pattern can be observed though, the wave form most likely become round and eye-opening height could result in small.
What do Rise Time and Fall Time mean ?
Rise Time and Fall Time are the terms which in general indicate the pulse wave form.
When the transition time of input optical power is very fast such as less than 100 ps, it expresses a swing speed of the output voltage.
Rise Time is the duration required to go up from 10 % to 90 % of the pulse height, and Fall Time is the duration required to go down from 90 % to 10% of the pulse height.
What is the maximum output voltage ?

What is the Maximum input optical power
Output voltage
The output voltage from LPD-1 increases in proportion to the optical power which is input to it. The conversion sensitivity is 500mV/mW ±10% against 1300nm at 50 Ω of termination. When incident optical power is 0.8mW or greater against 1300nm, it will saturate because the maximum swing-able output voltage is about 400mV.

Maximum input optical power
The maximum input optical power is injection optical power into the O/E converter at the saturation limit of the output voltage from the O/E. Maximum output voltage without saturation of LPD-1 and LPD-2 is 400mV when the load resistanse is 50 ohms.
Do you have the data of quantum efficiency of InGaAs ?
Quantum efficiency data of InGaAs
The PD implemented to LPD-1 is G6854-01 of Hamamatsu Photonics. No description about the quantum efficiency data is found in the data sheet though, the estimated quantum efficiencies at 1300nm and 1500nm are calculated as follows: At 1300nm : about 86%(0.9A/W) out of 100% (1.064A/W) At 1550nm: about 78% (0.95A/W) out of 100% (1.247A/W)
What is the Noise-Equivalent Power (pW/Hz^0.5). Noise equivalent power is converted value of the output noise density.
Quantum efficiency of DLP-2 ?
We do not have the quantum efficiency data of the DLP-2.
In terms of the quantum efficiency of the PD, please refer to the below.

Quantum Efficiency (This information refers to the document by Hamamatsu Photonics K.K. with permission.)
Quantum Efficiency is given the value ( percentage ) of the number of electrons or electron holes taken out as the optical current divided by the number of incident photons.
The relationship between Quantum Efficiency(QE) and Light Receiving Sensitivity (S) at a wavelength (λ) is shown as:
   λ: wavelength(unit: nm)
   S: Light receiving sensitivity at λ (unit: A/W)
Graviton measures the quantum efficiency of every PD (Photo Detector) equipped in the Graviton's DLP series converters and uses the best matching two PD to each DLP.
For your reference, the average Light receiving sensitivity(S) at 1310nm is 0.9834(A/W).
The average is given by the measured data of 20 pcs of PD to use for DLP-2.

The quantum efficiency is not officially calculated by Graviton but the estimated value is as follows, considering the average of 20 pcs of PD to use for DLP-2:

0.9834 x (1240nm/1310nm) x 100 ≈93.1 (%)
By using an optical fiber cable, is it possible the electrical signal from the measurement device which is remotely located such as in manufacturing line can be transmitted to measure locally ?

( In such a case, are there any limitations depending on S/N of cable and so on ?)
It is possible to use it as analog optical link, but there are two limitations.
(1) The lower limit of modulated frequency of Gravitino’s E/O converters is 100kHz.
In case configuring the analog optical link by using Graviton's E/O and O/E converters, as the lower limit of the modulated frequency bandwidth is 100kHz, the frequency lower than 100kHz cannot be transmitted, including direct current signal voltage as well. However, practically up to about 1kHz modulated frequency can be transmitted.

(2) The modulation sensitivities of Graviton's E/O converters are not exactly controlled.
The voltage amplitude and optical intensity amplitude which are input to Graviton's E/O converters vary among the products as they are not accurately controlled.
It is possible to use our E/O converters on purpose of confirming the quality of waveforms, but we do not recommend using them in order to transmit the absolute value of analog voltage.

Except the above-mentioned cases (1) and (2) and in case of using the bandwidth of between 100kHz and 1GHz, the combination of VL-670GI and SPA-2 or VL-670GI and SPD-2 is recommended. VL-670GI is the model which has less noise of the modulated light source. SPA-2 and SPD-2 have higher conversion sensitivity of 1000V/W than other models. Therefore, the combination of those will produce less attenuation of electrical signal.
Graviton provides MWL-TX & RX series of microwave link which can transmit analog signal from 2kHz to 3GHz with good S/N ratio. Please contact us.
We have LPD-1.
Can we observe 850nm with it ?
It is possible.
However, as LPD-1 is the O/E converter model which has a PD for long wavelength, note the sensitivity at 850nm is about 1/10 comparing the one at 1300nm.
Please tell us the application to transmit high frequency signal from Anechoic chamber using optical fiber cables. Graviton provides MWL-TX & RX series of microwave link which can transmit analog signal from 2kHz to 3GHz with good S/N ratio.
Please contact us.