JPH03148890A - Constituting method for single-mode light-pulse light source - Google Patents

Abstract

PURPOSE:To vary oscillation wavelengths at every longitudinal mode wave-length by directly modulating the intensity of a Fabry-Perot resonator type semiconductor laser by a periodic external signal, delaying one part of a light output generated for a modulation period or only by the integral multiples of the modulation period through a wave-length selective element and feeding back one part of the light output to the semiconductor laser. CONSTITUTION:Electric pulses for modulating a semiconductor laser are generated in a pulse generator 2 while being synchronized with a signal from a signal generator 1, and the signal is overlapped to bias currents from a DC current source 3, and input to a Fabry-Perot type semiconductor laser 4. Light pulses output from the laser 4 are operated at the branching ratio of 1:1 by a photo-coupler 5, and a feedback output is emitted once from a fiber through a delay single-mode optical fiber 6 and an element 7 for controlling deflection. The output light is converted into parallel beams by a collimator lens 8, and reflected by a diffraction grating 9 at a proper angle and fed back to the laser 4. Accordingly, oscillation wavelengths can be varied at every longitudinal mode wavelength of the laser, and the function of a single-mode light-pulse light source is given.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for configuring a single mode optical pulse light source used for high-speed optical transmission, wavelength dispersion measurement, and the like.

(Prior Art) Fields in which a single mode intensity modulated light source is required include the following.

(1) Ultra high speed (high bit rate)/long distance optical transmission (2)
High-precision chromatic dispersion measurement What the above two fields have in common is that due to the difference in group delay (chromatic dispersion) depending on the wavelength of the optical transmission medium, when using a multi-longitudinal mode laser, the transmission capacity and measurement accuracy are significantly reduced. It is to be restricted. Conventionally, single-mode intensity modulated light sources have adopted the so-called DFB (distributed feedback) structure or DBR (distributed black reflection) structure, which incorporates periodic refractive index changes within the semiconductor crystal instead of the Fabry-Bello resonator structure. It has been implemented and realized. Although stable single-mode oscillation can be obtained by these methods, the wavelength tuning range has also become narrower.

Therefore, when attempting to measure chromatic dispersion over a certain wavelength range, it is inconvenient that it is necessary to prepare a plurality of DFB lasers.

In addition, Er-doped optical fiber, which is a type of optical fiber optical amplifier that has been attracting attention recently, has a maximum gain at 1.54 μm, and commercially available OFFs manufactured for 1.55 μm
With B-Rade, it was difficult to adjust to the gain center.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for configuring an optical pulse light source for realizing a single mode light source that can change the oscillation wavelength of a semiconductor laser by using a selection element. .

(Means for Solving the Problems) The single mode optical pulse light source configuration method of the present invention converts a part of the periodically modulated output of a Fabry-Perot semiconductor laser that oscillates in multiple longitudinal modes into a modulation period The feedback path is synchronized with , and an optical element that selects only a single mode is inserted in the feedback path to achieve single mode oscillation.

Since the wavelength component selected by the wavelength selection optical element is fed back to the semiconductor radar, only its longitudinal mode is excited. When the oscillation of one mode grows, other longitudinal modes are suppressed due to the nonlinear effect inherent in lasers.

(Example) FIG. 1 is a diagram showing an example of the present invention, in which a commercially available semiconductor component called a semiconductor laser module was used. This integrates a semiconductor laser and an output fiber, and includes a photodiode for monitoring optical output that receives light from the other end face of the semiconductor laser that is not the output end face, and a cooling device for controlling the temperature of the semiconductor laser. The semiconductor laser is usually hermetically sealed.

For example, a semiconductor laser manufactured for 1.55 μm is
When attempting to oscillate in a single mode at 1.54 μm, which is the maximum gain wavelength of the r-fiber, the semiconductor laser must be cooled to around 0°C, and being hermetically sealed is important to prevent water droplets from forming on the laser end face. desired to avoid condensation.

Therefore, on the contrary, when trying to obtain a single mode near the room temperature oscillation wavelength, there is no particular need for hermetically sealing.

The operation of this embodiment will be explained with reference to FIG.

In synchronization with the signal from the signal generator 1, the pulse generator 2
Generates electrical pulses for semiconductor laser modulation. This signal is superimposed on the bias current from the DC current source 3 and is input to the Fabry-Perot semiconductor laser 4 . The bias current is adjusted to be slightly lower than the threshold current of the laser. The output optical pulse from the semiconductor laser 4 is sent to the optical coupler 5.
It is branched at. A branching ratio of approximately 1:1 works well.

The feedback output is emitted from the fiber via the delay single mode optical fiber 6 and the polarization control element 7. This output light is converted into a parallel beam by the collimating lens 8,
The light is reflected by the diffraction grating 9 having an appropriate angle, travels in the opposite direction along the predetermined optical path, and is returned to the semiconductor laser 4. The time from laser emission to return must be an integral multiple of the laser modulation period. The tolerance is approximately on the order of pulse width.

In addition, the polarization control element 7 adjusts the birefringence of this optical fiber feedback system to maximize the reflectance of the diffraction grating 9 and to ensure that the polarization of the output light of the semiconductor laser 4 and the feedback incident light are the same. do.

No. 211l shows the single mode spectrum thus obtained in comparison with the multimode spectrum without feedback.

A similar system can also be constructed without using the optical coupler 5. That is, one end face of the semiconductor laser can be used for feedback, and the other end face can be used for output only. The configuration in this case is shown in FIG.

(Effects of the Invention) As described above, by using the single mode optical pulse light source configuration method of the present invention, a single mode light source whose oscillation wavelength can be changed for each longitudinal mode wavelength of a semiconductor laser can be realized. As a result, it is possible to realize (1) a light source for high-speed optical transmission in which the transmission wavelength matches the zero-dispersion wavelength of the transmission line fiber, (2) wavelength tuning for narrow wavelength band optical amplifiers, and (2) a tunable wavelength light source for precision chromatic dispersion measurement.

[Brief Description of the Drawings] Figure 1 is a diagram showing an embodiment of the present invention, Figure 2 is a diagram comparing semiconductor spectra with and without optical feedback, and Figure 3 is a diagram showing a comparison of semiconductor spectra with and without optical feedback. The figure shows another embodiment of the invention. l... Signal generator 2... Pulse generator 3.
... DC current source 4 ... Fabry-Perot semiconductor laser 5 ... - Optical coupler 6 ... Delay single mode optical fiber 7 ... Polarization control element 8 ... Collimating lens 9 ... Diffraction grating patent applicant Nippon Telegraph and Telephone Corporation Agent Patent attorney Akira Sugimura Hidetoshi Patent attorney Oki Sugimura To Saku 71＼ l
l→←・・′1 κ 7

Claims (1)

[Claims] 1. A portion of the optical output generated by direct intensity modulation of a Fabry-Perot cavity semiconductor laser using a periodic external signal is delayed by the modulation period or an integral multiple thereof via a wavelength selection element and then fed back to the semiconductor laser. A method for configuring a single mode optical pulse light source.