Optics: measuring and testing – Range or remote distance finding – With photodetection
Patent
1987-06-12
1989-09-19
Arnold, Bruce Y.
Optics: measuring and testing
Range or remote distance finding
With photodetection
356334, G01J 318, G02B 2744
Patent
active
048675326
DESCRIPTION:
BRIEF SUMMARY
This application is related to my copending commonly assigned application Nos. 80,465 and 80,469 filed currently herewith.
The invention relates to a wavelength selection device and a method of selecting radiation centred on a particular wavelength.
It is important when using recently developed laser chips to be able to improve their performance by narrowing the range of wavelengths emitted by the chip. This has been done in the past by positioning a diffraction grating coaxial with the beam emitted by the laser chip and at such an angle to the impinging beam that a selected wavelength is reflected back along the axis towards the laser chip. This angle is the Bragg angle. It has proved quite difficult to do this in the past due to the cumbersome nature of the mounting arrangements which are required to support the diffraction grating particularly when compared with the small dimensions of laser chips.
In accordance with one aspect of the present provided by a torsion member mounted to the substrate; and control means responsive to control signals to cause the selection member to deflect, whereby radiation centred on a predetermined wavelength is selected from radiation having a number of wavelengths impinging on the selection member by setting the selection member at a predetermined angle to the incoming radiation.
The invention enables a deflectable wavelength selection member to be constructed on a much smaller scale than hitherto by using a microengineering technique thus reducing the problems previously encountered with conventional diffraction gratings.
In accordance with a second aspect of the present invention, a method of selecting radiation centred on a particular wavelength from an original beam of radiation comprising a number of different wavelengths comprises causing the original beam to impinge on a wavelength selection device according to the one aspect of the invention; and causing the wavelength selection member to deflect whereby only radiation having a wavelength centred on the selected wavelength is deflected through a predetermined angle.
Preferably, the wavelength selection member comprises a diffraction grating although other types of selection members could also be used. In the case of a diffraction grating, the surface of the torsion member may be ruled to define the grating.
Conveniently, the diffraction grating comprises a reflection grating although in some circumstances a transmission grating could also be used providing one or more apertures were provided in the substrate to enable transmitted radiation to pass through.
Preferably, the torsion member comprises a torsion plate which is conveniently integrally formed with the substrate. This latter arrangment can be achieved using conventional masking and etching techniques or laser etching techniques particularly where the material from which the substrate is formed is a single crystal of for example silicon when anisotropic etching techniques can be used. The integral arrangement is particularly useful since it reduces the number of separate parts involved and thus improves the integrity of the device.
In some examples, the device may further comprise a selective wavelength transmission member mounted adjacent the wavelength selection member and movable therewith, the selective wavelength transmission member permitting only certain wavelengths of impinging radiation to be transmitted therethrough.
With this arrangement, a two stage wavelength selection operation is carried out. The wavelength selection member (typically a diffraction grating) provides a coarse wavelength tuning element while the additional selective wavelength transmission member provides a fine tuning element.
Although the two members could be mounted separately on the substrate, preferably the members are connected together by one or more spacers.
Conveniently, the selective wavelength transmission member is positioned such that radiation is incident thereon prior to being incident on the wavelength selection member although an opposite arrangement is also f
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Arnold Bruce Y.
British Telecommunications public limited company
Edmondson David J.
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