THORLABS PICO D, User Manual

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2 System Description and Interfaces
This chapter intended as an aid when designing a system containing PICO D. In or-
der to assure that PICO D will operate correctly and at the given specifications, the
requirements regarding handling an operation given in this manual have to be met.
2.1 What is a tunable laser source (TLS)?
A Tunable Laser Source (TLS) is a laser whose output wavelength could be swept
(continuous or random access) over a certain, and usually quite wide, wavelength
range. The PICO D can be tuned over typically 110 nm (albeit depending on the ac-
tual model of PICO D) which is sufficient for covering both the C- and L- wavelength
bands used in fiber optical communications systems. The TLS can be thought of as
an optical equivalent of a conventional electrical sweep oscillator. The acronym ECL
(External Cavity Laser), which reflects the technical design of the laser, is some-
times also used for describing the TLS function. However the acronym TLS has a
wider meaning since an ECL not necessarily is tunable.
TLS’s are frequently used in various measurement applications where a recording of
a certain measure versus wavelength is performed. Each application requires de-
tailed knowledge on some or all parameters characterizing a TLS (
e.g. wavelength
range, side mode levels, spontaneous noise levels, line width, sweep characteris-
tics).
2.2 Brief system overview
PICO D, see Figure 2–1, is a Tunable Laser Source (TLS) based on a semiconduc-
tor laser mounted in a Littrow external cavity laser geometry. This tuning arrange-
ment allows high output power and large mode-hop-free tuning range.
The interface between PICO D and the user is analog. Analog voltages are used to
set the output wavelength and output optical power. By applying an analog voltage
to the interface the wavelength can be randomly tuned to any wavelength or con-
tinuously tuned (i.e. swept) between any wavelengths within the operational wave-
length range given in the specifications. The tuning is truly continuous due to the
construction of the tuning arrangement (i.e. no step motor drive). A stable voltage
source is required for supplying the analog control signals for setting output wave-
length and optical output power.
PICO D is fully controlled by its electronic control system and the user supplied ana-
log signals for setting output wavelength and optical output power. Furthermore,
PICO D requires an external DC power supply to be operational.