Newport NIRVANA Manuel utilisateur

USER’S GUIDE

1837 GHz – NIRVANA

High Speed auto-balanced

Photoreceiver

phone: (877) 835-9620

e-mail: [email protected] •

www.newport.com

These photodetectors are sensitive to electrostatic

discharges and could be permanently damaged if

subjected even to small discharges. Ground your-

self adequately prior to handling these detectors

or making connections. A ground strap provides

the most effective grounding and minimizes the

likelihood of electrostatic damage

Contents

Overview

Quick start

General Principles

Operation

Specifications

Customer Service

Warranty

Newport Corporation guarantees its products to be free of defects for one year from the date of

shipment. This is in lieu of all other guarantees, expressed or implied, and does not cover

incidental or consequential loss. Information in this document is subject to change without notice.

The New Focus logo and symbol are registered trademarks of Newport Corporation

Document Number 90099917 Rev. A

Introduction

Overview

The Newport Model 1837 auto-balanced photoreceiver consists of two photodiodes followed by RF

amplifiers that generate an output voltage proportional to G1·I1 – G2·I2. G1 is a fixed transimpedance

while gain G2 is automatically controlled or manually adjusted to reject common mode.

The Quick Start and General Principles sections below give an overview of setting up the photoreceiver

and understanding its principles and design. The chapters that follow give detailed operating instructions

and specifications.

Balanced photodetection is a commonly used method when an optical measurement requires increased

signal-to-noise ratio. A balanced photoreceiver consists of two well-matched photodiodes configured so

that their photocurrents subtract and common-mode noise is canceled

To eliminate the problems associated with manually balancing the reference and signal beams the GHz

Nirvana1837 is an auto-balanced photoreceiver with a built-in low-frequency feedback loop that

controls the electronic gain of one of the receivers and maintains automatic balance between signal and

reference arms.

Quick Start

The following parts are supplied with the Model 1837 auto-balanced photoreceiver:

•Model 0923 3-pin to 3-pin power cable

•Model 0924 3-pin to banana connector power cable

•Model 0907 M-SMA to M-BNC cable

•Model 0927 F-SMB to M-BNC cable (x2)

Electrical cables of greater than 3 meters in length should not be used with the 1837 model

The steps on the following pages describe the basics of setting up and using the photoreceiver. The

Operation chapter contains more detailed information.

1. Use one of the supplied power cables to connect the photoreceiver to a 15-volt power source that can

supply 200 mA.

For the Newport Model 0901 power supply, use the 3-pin connector-to-3-pin connector cable. For other

power supplies, use the 3-pin connector-to banana plug power cable.

When using the 3-pin connector-to-banana plug cable, take care to hook up the banana plugs as follows

to avoid damaging the photoreceiver: Red = +15 V, Green = Ground, Black not needed,.

2. Mount the photoreceiver to your optical table. A pair of 8-32 and a pair of M4-threaded holes are

located on the bottom of the unit. (Figure 2)

3. Connect the optical source to one or both optical inputs. (Figure 2 ) Use single mode fiber with

FC/APC angle polished connector.

The optical power must remain below the absolute

maximum power listed in Table 1.

Exceeding the maximum power can damage thephotodiode and the amplifier.

4. Use the low-frequency M1 and M2 outputs to check and adjust the optical inputs so that the output

powers are in the desired 0–1 V range. ( Table 1 )

5. Finally, connect the RF Output SMA connector to the desired load or instrument via a 50Ω coaxial

cable. Set controls to MANUAL and G2 = G1 first until reading the signal from the RF Output. The

use AUTO or MANUAL MODE and G2 control as desired.

General Principles

The Newport Model 1837 auto-balanced photoreceiver consists of two photodiodes followed by RF

amplifiers that generate an output voltage proportional to G1·I1 – G2·I2. G1 is a fixed

transimpedance while gain G2 is automatically controlled or manually adjusted to reject common

mode.

A functional block diagram of the auto-balanced photoreceiver is shown in Figure 1, and a

mechanical drawing is given in Figure 2.

Figure 1: Functional block diagram of the Model 1837. The entire package is shielded to eliminate noise

pickup.

Low-frequency Monitor Outputs

In addition to the RF output, the balanced photoreceiver has two low-frequency monitor outputs, M1 and

M2. These monitor outputs can be used to help align light onto the photodiodes and to perform low

frequency diagnostics. The monitor outputs have SMB connectors, and an SMB-to-BNC cable is

provided with the photoreceiver. Monitors M1 and M2 characteristics are given by the technical Table 1

at the end of this manual.

Responsivity and Input Power

The Model 1837 uses a InGaAs photodiodes. Figure 3 shows the typical responsivity of the photodiodes.

To avoid damage to the amplifier, never exceed the input current of 1mA or 1 V at M1,

M2 or both

0.2

0.4

0.6

0.8

900 1000 1100 1200 1300 1400 1500 1600

Wavelength, nm

Responsivity , A / W

Figure 3: Typical responsivities InGaAs PIN photodiodes in the 1837. The amplifier has a maximum

input current of 1 mA or 1-Volt at M1, M2 or both. To avoid damage to the amplifier, never exceed this

input current.

-40

-35

-30

-25

-20

-15

-10

-5

1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09

Frequency, Hz

Norm Frequency response, dB

Gain, Bandwidth and Noise

The RF amplifiers in Figure 1 present typical AC coupled gains of G1 and G2 and amplify photodiodes

currents I1 and I2. G1 is fixed to typically 40 000 Volts/Amp AC and G2 can be automatically or

manually set to values larger or smaller than G1. The amplifier is AC coupled

with a 100-kHz low-frequency roll-off.

The RF output stage can typically drive up to 0 dBm at -20dB total harmonic distortion (THD) into a 50-

Ω load. To maximize signal fidelity keep the output signal level below -10dB.

The 3dB RF bandwidth exceeds 300 MHz for the Model 1837. Figure 4 shows typical frequency

response.

Fig 4 –Typical frequency response of INPUT 1 (G1 – relative ). The FR on INPUT 2 can be adjusted at

least +4dB or -4dB with respect to the trace shown.

The noise is frequency dependent and has typical value expressed as noise-equivalent power (NEP)

referred to 1837 input and shown on Fig 5.

The output AC voltage plus internal noise from 1837 can be approximated as:

BWNEP 











 2

1CMRR

SGOUPUT , where BW is the noise equivalent bandwidth in Hz of

the instrument connected following 1837.

Fig 5 – Input Noise Equivalent Power (NEP) referred to the either INPUT 1, 2 of 1837 for MANUAL

mode to 1GHz.

auto-balanced and Manual Balanced Modes

When in auto-balanced Mode (switch to AUTOBAL) 1837 Photoreceiver has a patent pending control

logic ( Fig 1) that detects signals on Input 1 and Input 2 in the range 30KHz to 1MHz (common mode).

By computing the ratio between them it automatically generates a voltage V to control G2 and equalize

G2·I2 to G1·I1 in that frequency range and suppress it at the output V0.

In order to properly utilize 1837 the fluctuations in the common mode signal in that frequency range have

to exceed about 10uW-p-p in the 30 KHz to 1 MHz range, like amplitude fluctuations from a swept

wavelength laser.

When the minimum common mode signal conditions are not met, it is possible to switch to a MANUAL

MODE and manually set G2 through the voltage V.

Figure 6 shows the Common Mode Rejection Ratio – CMRR – when 1837 is used in AUTOBAL mode.

Figure 7 shows the gain range of G2 compared to G1 when 1837 is set to MANUAL mode.

FIG 6 – Typical CMRR for AUTOBAL operation mode in 1837.

Fig 7 – Gain range for G2in MANUAL mode. The frequency flatness of G2compared to G1is better than

2 dB over the full 1 GHz range.

Operation

Connecting the Power Supply

The balanced photoreceiver’s power supply connector is a shielded 3-pin connector. This should be

connected to a +15-Volt power supply capable of providing a current of 200 mA.

(We recommend the Newport Model 0901 power supply.)

Two different power cables are shipped with the photoreceiver: a Model 0923 3-pin connector-to3-pin

connector cable, for use with the Newport power supply, and a Model 0924 3-pin connector-to banana

plug cable, for use with other power supplies.

Using a Newport Power Supply

If you have a Newport Model 0901 power supply, use the Model 0923 3-pin connector-to-3-pin

connector power cable to connect the photoreceiver to one of the power supply’s 0.3-A 3-pin connector

outputs. Be careful to align the notches on the connectors when attaching the cable. If the connectors are

not mated correctly or the pins are bent, the photoreceiver may be damaged.

Do not use the power supply’s 0.1-A banana-jack output, since

it does not provide enough current for the photoreceiver.

Using Another Power Supply

Use the Model 0924 3-pin connector-to-banana plug power cable when working with a power supply

other than the Newport Model 0901. Be sure to hook up the banana plugs correctly, or the

photoreceiver can be damaged. The convention for the three banana plugs is as follows: Red = +15

V, Green = Ground. Black = not needed.

Be careful to align the notches on the connectors when attaching the 3-pin connector end of the cable to

the photoreceiver. If the connector is not mated correctly or the pins are bent, the photoreceiver may be

damaged.

Checking the Power Connection

The photoreceiver draws approximately 200 mA on the +15-V line. If the current drawn is 0 mA, the

power supply cable may have a bad connection. If the current draw is

greater than 200 mA, then the cable could be shorted or there may be an internal problem with the

photoreceiver. Contact Newport for support and, if necessary, instructions on returning the unit.

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