Patent EP0108562A1 successfully refreshed from Google Patents.
EP0108562A1
Expired / Lapsed
EP
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Controlling lasers
Assignee: British Telecommunications PLC
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Filing: 1983-10-27
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Granted: —
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Expires: 2003-10-27
Abstract
Abstract A method and apparatus for controlling an external cavity of a semiconductor laser to maintain its emission in a single longitudinal mode. The length of the external cavity is varied by an electromagnet acting on ferrogmagnetic material 6 attached to a copper foil reflector 4. Total optical power output of the laser is monitored and single longitudinal mode operation is achieved by maximising the power output. An active technique employs modulation of the reflector position about a mean value. The magnetic manipulation of the reflector may find application in other laser systems, e.g. gas lasers.
Inventors
- 👤 Keith Robert Preston
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 07:36
CPC Classifications
H; H01; H01S; H01S5/00; H01S5/10; H01S5/14; H01S3/00; H01S3/10; H01S3/13; H01S3/139; H01S3/1398; H01S5/06; H01S5/068; H01S5/0683; H01S5/06837
Claims Analysis
Total Claims: 16
Claim 1
Independent Claim
53 words
A method of controlling a semiconductor laser for single longitudinal mode operation, the laser having an external cavity defined by an external reflector, characterised in that the method comprising sensing the radiation output power of the laser and adjusting the optical path length of the external cavity to maximise the radiation output power.
Claim 2
Independent Claim
53 words
A method of controlling a semiconductor laser for single longitudinal mode operation, the laser having an external cavity defined by an external reflector, characterised in that the method comprising sensing the radiation output power of the laser and adjusting the optical path length of the external cavity to maximise the radiation output power.
Claim 3
Dependent Claim
28 words
A method of controlling a semiconductor laser as claimed in claim 1 wherein the optical path length of the external cavity is adjusted by moving said external reflector.
Claim 4
Dependent Claim
112 words
A controlled semiconductor laser adapted to operate in a single longitudinal mode, comprising an external reflector (4) mounted with respect to a facet of the laser (2) to define an external cavity, characterised in that the laser includes means (6,7,8) for adjusting the optical path length of the cavity, means (9) operative to monitor the radiation output power of the laser and to produce a control signal representative of the magnitude thereof, and signal processing means (13,14,15) fed with said control signal and arranged to control said adjusting means to vary the optical path length of said cavity such that the value of the radiation output power of the laser is maximised.
Claim 5
Dependent Claim
112 words
A controlled semiconductor laser adapted to operate in a single longitudinal mode, comprising an external reflector (4) mounted with respect to a facet of the laser (2) to define an external cavity, characterised in that the laser includes means (6,7,8) for adjusting the optical path length of the cavity, means (9) operative to monitor the radiation output power of the laser and to produce a control signal representative of the magnitude thereof, and signal processing means (13,14,15) fed with said control signal and arranged to control said adjusting means to vary the optical path length of said cavity such that the value of the radiation output power of the laser is maximised.
Claim 6
Dependent Claim
30 words
A controlled semiconductor laser as claimed in claim 3 wherein said reflector (4) is mounted for translational movement and the adjusting means includes means (6,7,8) for accurately moving said reflector.
Claim 7
Dependent Claim
101 words
A controlled semiconductor laser as claimed in claim 4 wherein the means for accurately moving the external reflector is further controlled to cause the external reflector (4) to undergo a small oscillatory motion about a mean distance from said laser facet, the signal processing means (13,14,15) being operative to compare said control signal with respect to the oscillatory position of the reflector (4) and to cause said means (6,7,8) for moving the external reflector to adjust the mean position of the reflector (4) to minimise the value of the rate of change in radiation output power with respect to reflector position.
Claim 8
Dependent Claim
87 words
A controlled semiconductor laser as claimed in claim 5 including further signal processing means fed with said control signal and including a comparator (11) operative to compare the value of the control signal with a reference signal, and produce an output signal according to the difference between them, the output signal from the comparator (11) being used to control the laser bias to such that the control and reference signals are equalised and hence the radiation power output of the laser (2) maintained at a predetermined value.
Claim 9
Dependent Claim
61 words
A controlled semiconductor laser as claimed in any one of claims 4 to 6 wherein said external reflector (4) includes or has in moving association therewith, magnetically-responsive material (6), and said means for accurately moving the reflector comprises an electromagnet (7,8) producing a controlled magnetic field to move said reflector (4) by the magnetic force on said magnetically responsive material (6).
Claim 10
Dependent Claim
80 words
A controlled semiconductor laser as claimed in claim 7 wherein the external reflector (4) includes a reflecting portion (5) within a larger resilient mounting (3), the reflector (4) being fixed at a position on its surface with respect to said laser facet, said magnetic force having a line of action displaced from said one position, so that, when applied, the reflector (4) is caused to flex and thereby move the reflecting portion (5) translationally with respect to the laser facet.
Claim 11
Dependent Claim
16 words
A controlled semiconductor laser as claimed in claim 8 wherein the reflecting portion (5) is concave.
Claim 12
Dependent Claim
20 words
A controlled semiconductor laser as claimed in claim 8 or claim 9 wherein the external reflector (4) comprises metallic foil.
Claim 13
Dependent Claim
67 words
A variable length external cavity for a laser comprising an external reflector (4), defining the length of the cavity, characterised by including or having in moving association therewith, magnetically-responsive material (6), the position of the reflector (4) with respect to a mirror of the laser (2) being accurately controllable over a range of distances by an electromagnet (7,8) producing a magnetic force on said magnetically-responsive material (6).
Claim 14
Dependent Claim
67 words
A variable length external cavity for a laser comprising an external reflector (4), defining the length of the cavity, characterised by including or having in moving association therewith, magnetically-responsive material (6), the position of the reflector (4) with respect to a mirror of the laser (2) being accurately controllable over a range of distances by an electromagnet (7,8) producing a magnetic force on said magnetically-responsive material (6).
Claim 15
Dependent Claim
90 words
A variable length external cavity for a laser as claimed in claim 11 wherein the external reflector (4) includes a reflecting portion (5) within a larger resilient mounting (3), the reflector (4) being fixed at one position on its surface with respect to the mirror of the laser (2), said magnetic force having a line of action displaced from said one position so that, when applied, the reflector (4) is caused to flex and thereby move the effective reflecting portion (5) translationally with respect to the mirror of the laser.
Claim 16
Dependent Claim
26 words
A variable length external cavity for a laser as claimed in claim 11 or claim 12 connected to define an external cavity of a gas laser.
References Cited (Backward Citations)
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