Hans-Ulrich Pfeiffer

Further development of high-power pump laser diodes

AlGaAs/InGaAs based high power pump laser diodes with wavelength of around 980 nm are key products within erbium doped fiber amplifiers (EDFA) for todays long haul and metro-communication networks, whereas InGaAsP/InP based laser diodes with 14xx nm emission wavelength are relevant for advanced, but not yet widely-used Raman amplifiers. Due to the changing industrial environment cost reduction becomes a crucial factor in the development of new, pump modules. Therefore, pump laser chips were aggressively optimized in terms of power conversion and thermal stability, which allows operation without active cooling at temperatures exceeding 70°C. In addition our submarine-reliable single mode technology was extended to high power multi-mode laser diodes. These light sources can be used in the field of optical amplifiers as well as for medical, printing and industrial applications. Improvements of pump laser diodes in terms of power conversion efficiency, fiber Bragg grating (FBG) locking performance of single mode devices, noise reduction and reliability will be presented.

Compact 1.3 W green laser by intracavity frequency doubling of a multi-edge-emitter laser bar using a MgO:PPLN crystal

A compact green laser of 1.3 W output at 534.7 nm is generated by intracavity frequency doubling (ICFD) of a 49 edge-emitter laser bar using a MgO-doped (PPLN) bulk crystal. The measured M(2) values of green beam are 12.1 and 2.9 along the slow and fast axes, respectively. To our knowledge, this is the first demonstration of the ICFD of multi-edge-emitters laser bar.

Broad area single emitter (BASE) modules with improved brightness

High power pump modules are used for industrial as well as telecom applications such as for fiber lasers and cladding pumped erbium doped fiber amplifiers (EDFA) [Lichtenstein, N., et al., 2004]. Key element of a pump module is a single emitter laser diode, which normally has an aperture of around 90 mum, in order to provide best coupling into an optical multi-mode fiber with a 105 mum core diameter. Increasing the brightness of the pump module lends additional flexibility in the design of fiber lasers and amplifiers and enables higher output power. In this communication we report on two approaches to increase the brightness of our latest generation of high power pump modules. Within the first approach the electro-optical performance of the single emitter laser diode is improved by optimizing Bookhams mature chip technologies such as InGaAs/AlGaAs structures grown by MBE, the ridge-waveguide manufacturing process, the E2 facet passivation and the mounting technology. The combination of improved chip design and new coupling scheme leads to reliable broad area modules with outstanding brightness.

465 nm laser sources by intracavity frequency doubling using a 49-edge-emitters laser bar

A compact blue laser was generated by intracavity frequency doubling based on quasi-phase-matched second-harmonic generation (SHG) in a MgO-doped periodically poled lithium niobate bulk crystal. A 49 single-transverse-mode edge-emitters laser bar with antireflective coating was used as a pump source. An optical output power of 1.2 W SHG of blue lights at 465 nm is generated at 45 A injection current, equivalent to an overall wall-plug efficiency of 1.33%.

9xx high power pump modules

In this communication we present the characteristics of Bookhams MU7-9xx-01 laser module with multimode fiber output. This latest generation of our multimode modules is designed for light output power of up to 7 W in uncooled operation in the wavelength range between 915 nm and 975 nm. The key element of the module is our new SES8-9xx-01 broad area single emitter. These high power lasers in the 9xx nm wavelength range show a high slope efficiency of up to 1.2 W/A in CW room temperature operation. High efficiency combined with low threshold current and low operation voltage result in a maximum wall plug efficiency of above 65%. Almost 4000 h lifetest data at accelerated conditions are available for the laser diodes. The data give estimated reliability values of below 5 kFIT at operating conditions (between 8 A and 8.5 A injection current at up to 35°C heat sink temperature). The robustness of the new lasers is also illustrated by the fact that no catastrophic mirror damage was observed up to 22.5 W of light output power. The low divergence of the laser beam allows coupling into multimode fiber with 0.15 or 0.22 numerical aperture (NA) with a coupling efficiency above 90% at operation condition. Maximum ex-fiber light output powers of 11.5 W are shown. On module level around 2000 h lifetest data are accumulated without any failure or sign of degradation.

Blue light generated by intra-cavity frequency doubling of an edge-emitting diode laser with a periodically poled LiNbO3 crystal

We demonstrate for the first time to our knowledge intra-cavity frequency doubling (ICFD) of an edge-emitter diode laser using a 10 mm-long 5.0 microm periodically poled LiNbO(3) (PPLN) crystal. An optical output power of 33 mW second harmonic blue light at 490.5 nm is generated at 1.0 A injection current, equivalent to an overall wall-plug efficiency of 1.8%. The measured M(2) values of blue beam are 1.7 and 2.4 along the fast and slow axis.

Performance and reliability of pulsed 1060 nm laser modules

We report on reliable single-mode laser modules at 1060 nm used in pulsed operation for efficient seeding of fiber amplifiers. The modules incorporate InGaAlAs single quantum well diodes with a design inherited from telecom qualified devices. Pulse parameters can be widely varied with laser intrinsic modulation capability in GHz range. 2.5 W peak power is exhibited in a single-mode fiber at a current of 5 A with 200 ns pulses. Reliability is proven by lifetest in pulsed operation up to 3.5 A. Wavelength stabilization with fiber Bragg gratings is obtained over a wide range of operating conditions.

980 nm pump laser module with 750 mW output power

A new generation 980 nm pump laser module with a fiber output power more than 750 mW is presented. The module uses our generation-08 (G08) pump laser chip, which is designed for high output power and high reliability. The pump laser is stabilized by a fiber Bragg grating (FBG). A special thermo-electric cooler (TEC) is built into the package in order to enable operation of the device at high laser output powers.

Versatile 1 W narrow band 976 nm and 1064 nm light sources

We report on development of novel curved waveguide (CWG) laser devices, where the emission wavelength centered at ~976 nm is stabilized to a 20 dB bandwidth of less than 100 picometer by using fiber Bragg gratings (FBG). Radiation from the curved waveguide laser is coupled using an anamorphic fiber lens into a single mode polarization maintaining fiber containing the FBG, the latter acting as a front reflector. The high power gain chip is based on Oclaros InGaAs/AlGaAs quantum well laser. Use of the curved waveguide geometry allows to eliminate residual reflections in the optical path of the cavity, which is formed by the rear chip facet and the FBG. It is well known that additional reflections lead to significant deterioration of the spectral and power stability. The devices, assembled in telecom type housings, provide up to 1 W of low-noise and kink-free CW power. In addition pulse operation in nanosecond range is also investigated. The spectral stabilization time to the wavelength of the FBG is limited by the external cavity roundtrip of ~2 ns. A side mode suppression ratio of about 40 dB and higher is achieved for pulsed and CW operation. Results are also presented for a device at 1064 nm. Numerous applications can be envisioned for these devices. For instance devices with high power and ultranarrow spectral bandwidth allow greater flexibility in the choice of parameters for frequency conversion applications. In pulsed mode the device can be used in the special sensing applications where spectral stability is crucial.

Compact intracavity frequency doubled diode laser at 465 nm

Intra-cavity frequency doubling (ICFD) of an extended cavity 49-emitters edge-emitting laser bar has been demonstrated in a quasi-phase matching MgO-doped periodically poled lithium niobate (MgO: PPLN) bulk crystal. A maximum of 1 W of second-harmonic light at 465 nm is generated at an operating injection current of 45 A with the optimal phase-matching MgO:PPLN temperature of 50.4 °C. To increase the efficiency further, careful design of the lens used on the fast and slow axis beam waists and use of lower-temperature MgO:PPLN planar-waveguide array can be considered.