With over 20 years of Optoelectronics knowledge, we conduct cutting edge research for clients around the world.


Acoustic Camera

OptoSignal is currently investigating the feasibility of developing an acoustic camera, to image the sources of sound, and particularly noise, within a narrow and selectable frequency band from systems where it can be difficult to pinpoint the exact sources of the noise.

The Approach

OptoSignal is using a 2D array (typically 8 x 8) of acoustic sensors, such as the new MEMS IC microphones, which are small, sensitive (62db SNR) and have a bandwidth to 15 kHz. Each sensor is connected to a 24 bit Analog-to-Digital converter IC with a sampling rate of 96 ksps, taking advantage of the recent improvements that have taken place in this technology.

The signal sampling, typically at 37.5 ksps, is synchronised through the use of a common clock that is distributed to each sensor node, with the sampled data being stored locally, thus allowing an arbitrarily large sensor array to be used without incurring data transfer limitations.

The sampled data memory at each node needs to be a modest 1 Mbit, to store at least one second's worth of sampled data. The microprocessor at each node is connected to the four adjacent nodes, to allow the stored data at each node to be transferred to the designated node that is connected to a Personal Computer for subsequent data processing.

A novel aspect of this investigation is the synchronisation of the acoustic sampling with optical imaging, where we synchronise 1,024 acoustic samples, for example, with every image from a machine vision camera operating at a triggered frame rate of 36 fps. The ability to time step, frame by frame, through overlapping displays of the acoustic and the digital images will help to identify sources of impulsive noise.

Civilian Applications for Active Acoustic Imaging

Image the acoustic qualities of a concert hall

Use this system in an active difference detection mode, to detect intruders

Derive a real time 3D acoustic representation of the area in front of a robotic vehicle to enable the robot to avoid a collision with any solid object. (Note that shadows, often a problem with vision systems, would clearly not be a problem, and day / night operation is supported. Furthermore, there is no danger of any laser radiation, since the sensing is acoustic)

Test Fixtures

These are six test fixture products currently available from OptoSignal Limited

    1. 74001 E1P/O1P test fixture
2. 74003 screw grinding tool
3. 74004 test fixture bracket
4. 74005 air coplanar probe test fixture
5. 74006 air coplanar probe bracket
6. 74007 optical fibre: GRIN lens assembly

E1P/O1P Test Fixture

The OS 74001 consists of one electrical port and one optical port. This test fixture:

1. is usable from d.c. to at least 20 GHz in a 50 ohm characteristic impedance environment
2. can be mounted on an OptoSignal temperature controlled stage, the temperature of which can be varied from 10 °C to 100 °C
3. is made from gold plated highly thermally and electrically conductive CuTe (copper tellurium)
4. the active component is mounted on a thermally conductive AlN substrate, with a precision thin film technology 50 ohm characteristic impedance microstrip line
5. can be used to determine the small signal and large signal characteristics of photodiodes and laser diodes.

Photodiode Characterisation

The photodiode is mounted at the end of a microstrip line on AIN silver epoxy, or a AuSn preform. Modulated light from an optical fibre (using either a lensed fibre or a GRIN lens at the end of the fibre) is focussed on the active area of the photodiode, with the photodiode reverse biased through the use of a bias TEE.

The electro-optic S21 response of the photodiode can then be measured through the use of an electro-optic network analyser.

Laser Diode Characterisation

The laser diode is mounted at the end of a microstrip line on AIN through the use of a thermally conductive AuSn preform. In order to correctly terminate the impedance of the microstrip line, two bond wires from the top of the laser diode are attached to the top contact of two, 100 ohm half-wrap-around-ground chip resistors.

The laser diode can be biased through the use of a bias TEE. The heat sink temperature of the laser diode can be changed through the use of an OptoSignal temperature controlled stage. The small signal electro-optic response of the laser diode can then be determined through the use of an electro-optic network analyser.

Screw Grinding Tool

The OS 74003 screw grinding tool is required to flatten the bottoms of the M2.5 conical head screws used in the OS 74002 test fixture.

This tool is used to flatten the bottom of the M2.5 conical head screws. Screws with flattened heads are recommended for use in the construction of this test fixture.

Test Fixture Bracket

The OS 74004 test fixture bracket is used as an intermediate mount for the OS 74001 and OS 74002 test fixtures and the METRIC versions of the high precision Melles Griot XYZ translation stages. The test fixture is made from 3mm thick gold plated brass.

Additionally, printed circuit boards, on which photodiodes have been mounted, can be securely held in place, vertically or horizontally. For example, the electrical signal from the PCB can be extracted through the use of SMA edge connectors, with the light for the photodiode being introduced through the use of a lensed optical fibre securely held by an OptoSignal fibre holder mounted on a precision Melles Griot XYZ translation stage.

Air Coplanar Probe

This test fixture is for use with test devices being probed electrically through the use of air coplanar probes (ACP), such as the Cascade Microtech GSG probes.

This test fixture:

1. Is usable from d.c. to the limits of the probe system used
2. Can be mounted on an Optosignal temperature controlled stage, the temperature of which can be varied from 10 °C to 100 °C
3. Is made of gold plated highly thermally and electrically conductive CuTe (copper tellurium)
4. The active component is mounted either directly on the block, or on a thermally conductive AlN substrate
5. Can be used in the measurement of the small signal and large signal characteristics of photodiodes and laser diodes

Air Coplanar Probe Bracket

The OS 74006 is a bracket for securely holding the Cascade Microtech GSGxxx air coplanar probes to the precision MERIC Newport aluminium 460 and steel 462 XYZ translation stages. The bracket is made of gold plated Tbrass.

Four M6 (6 mm metric) screws are used to hold the bracket to the XYZ translation stage and three M4 (4 mm) screws are used to hold the air coplanar probe to the bracket.

Optical Fibre: GRIN Lens Assembly

The OS 74007 fibre assembly consists of a single mode fibre optic collimator and a co-linear GRIN lens, to achieve the focusing of the light from the fibre onto a point object, such as a photodiode, or the efficient collection of light from a laser diode.

The diameter of the gold plated brass assembly is 6.0 mm, specifically designed to fit in a Melles Griot fibre holder assembly, which in turn fits on a precision Melles Griot XYZ positioner.

Laser Diode Characterisation

Employees at OptoSignal have many years of experience in the characterisation of semiconductor laser diodes, including:

1. measurement of static electro-optic charcateristcis of a laser diode
2. measurement of the dynamic electro-optic characteristics of a laser diode up to 20 GHz
3. extraction of equivalent circuit models for the laser diode


OptoSignal designs the following types of optoelectonic circuit:

1. high speed high gain low noise Transimpedance Amplifier (TIA) circuit
2. high speed laser driver circuit
3. stabilised low noise laser diode bias current for coherent optics work
4. parallel 16 channel InGaAs photodiode array and receiver module