JPH01145885A - Optical amplifier - Google Patents

Abstract

PURPOSE:To amplify a high-speed optical signal with good linearity and to facilitate construction of an optical system, by providing a structure in which an optical input travelling forward and backward only once in a resonator is emitted as an optical output, a means for passing only the optical input, and a means for passing the optical output selectively. CONSTITUTION:While a bias current higher in its value than a threshold current is supplied from a current source 104 to a semiconductor laser, an optical input is supplied from outside to a semiconductor laser 101. An optical isolator 108 allows light to pass only from left to right on this figure. Light inputted into an active layer 107 travels from left to right on the figure while being amplified, and it is reflected on a high reflection factor film 103. The reflected light travels again in the active layer 107 and is amplified and reaches a low refection factor film 102. However, the light goes out with almost no reflection. Accordingly, amplification is performed only in one forward and backward travelling. The travelling route of the optical output 112 emitted is bent at 90 degrees at a deflection beam splitter 109, and then the light is made to pass through a wavelength filter 113. Only light with a wavelength of the optical output 112 is made to selectively pass through the wavelength filter.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical amplifier using an optical gain medium made of a semiconductor in a system that uses light as a signal, such as optical communication or optical information processing.

2. Description of the Related Art Communication and information processing that uses light as a signal, such as optical communication and optical computing, are expected to be put to practical use because light is fast and is not easily affected by electromagnetic induction. However, since the signal light is attenuated by absorption, scattering, etc. in the transmission path, it is necessary to amplify it during transmission. One possible means of optical amplification is
Optical amplification using a semiconductor laser amplifier (for example, Electronics Letters, Vol. 23, No. 2o).

1052A-1053).

However, in a typical semiconductor laser amplifier, as the power in the active layer increases due to an increase or decrease in the photon density of the optical input into the laser cavity, the photon density of the optical input into the resonator also increases. Therefore, stimulated emission induced by optical input also increases.

However, as long as laser oscillation continues, the carrier density remains fixed at Nth. However, since the bias current is constant, the total gain remains unchanged, so
When the photon density of the optical input into the resonator reaches Pl, the gain used for amplification becomes too large, laser oscillation stops, and the carrier concentration begins to fluctuate.

FIG. 4 shows this situation. If the value of optical input when reaching Pi is El, the optical output vs. optical input characteristic is the sixth
As shown in the figure, a linear response is obtained in the region of optical input below Ei.

Problems to be Solved by the Invention However, according to the above configuration, the incident light input goes back and forth within the resonator several times before being output. If the resonator length is 300 microns, it will take about 6 to 7 picoseconds for round trip.
Overall, a time delay of several tens of picoseconds to about 10 picoseconds occurs, making it difficult to amplify high-speed optical signals of several gigabits per second or higher.

Means for Solving the Problems In order to solve the above problems, the present invention provides a current source for a semiconductor laser having a low reflectance coating on one end face and a high reflectance coating on the other end face. When a bias current higher than the threshold current is supplied to generate laser light, the optical input injected from the end face with the low reflectance coating travels back and forth through the resonator only once and is emitted as optical output. The main focus is to be

In addition to the above-mentioned configuration, the present means includes means for passing only the optical input but not the optical output, and means for selectively transmitting only the optical output out of the laser beam and the optical output. Ru.

Effects According to the above-described configuration, the optical input is emitted as an optical output after just one round trip through the resonator, so it can sufficiently cope with amplification of high-speed optical signals of several gigabits per second or more. Furthermore, since light input and output is performed only through one end face, the configuration of the optical system is facilitated. Furthermore, the low reflectance coating also increases the threshold carrier density (th) and shortens the carrier lifetime, which also contributes to good high-speed response.

Example FIG. 1 shows a block diagram of an embodiment based on the present invention.

101 is a semiconductor laser, and its two end faces are coated with a low reflectance film 102 and a high reflectance film 1o3, respectively. For example, the reflectance is 0.1% and 99%, respectively. A bias current higher than the threshold current is supplied to this semiconductor laser from a current source 104. Now, since the similar loss is increased by the end face coating, the threshold current becomes about twice as large as before the coating. Furthermore, the threshold carrier density has increased nearly twice, and the lifetime of carriers has become shorter.

In this state, the optical input 106 is input from the outside to the semiconductor laser 1o1.
Inject into. Reference numeral 108 denotes an optical isolator, which is set to pass light only from left to right in the drawing. Note that the optical input 105 consists of polarized components that pass through a polarizing beam splitter 109. 110 is a Faraday rotation element, and the polarization plane of the optical input 106 is rotated by 46 degrees when passing through this element. Thereafter, the optical input 105 is focused by a lens 111 onto the end face of the semiconductor laser 1o1. The light injected into the active layer 107 travels to the right from the top of the drawing while being amplified and is reflected by the high reflectance film 103. The reflected light returns to the active layer 1
07, the light is amplified and reaches the low reflectance film 1o2, but it is emitted without being reflected at all. Therefore, amplification with this configuration is performed in only one round trip, and does not repeat round trip as in the conventional example. Now, the emitted light output 112 is rotated by 46 degrees again by the Faraday rotator 11o so that the plane of polarization becomes orthogonal to the light input 105.

Therefore, the path of the light is bent by 90 degrees by the polarizing beam splitter 109, and then passes through the wavelength filter 113. The wavelength filter selectively passes only the wavelengths of the optical output 112.

Therefore, the oscillation light 106 of the semiconductor laser 101 is blocked by the wavelength filter 113 or the optical isolator 108.

As mentioned above, according to the above configuration, the time during which the optical input is amplified is approximately 6 hours, which is equal to the time for one round trip through the resonator.
It is very short, about 7 picoseconds. Furthermore, since the carrier lifetime is short, it is suitable for amplifying high-speed optical signals. Furthermore, since laser oscillation is used, there is no fluctuation in carrier concentration and a linear response can be achieved. Therefore, an optical input consisting of a signal of, for example, 1 gigabit per second as shown in FIG. 2 can be output as amplified light without waveform deformation or the like.

Effects of the Invention According to the present invention, an optical amplifier that can amplify high-speed optical signals with good linearity can be constructed. Furthermore, since light can be input and output from only one side of the semiconductor laser, the configuration of the optical system is facilitated.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the optical amplifier of the present invention, Fig. 2 is a waveform diagram of optical input and optical output of the embodiment based on the present invention, and Fig. 3 is a block diagram of a conventional optical amplifier. , FIG. 4 is a diagram showing the relationship between the carrier density and the optical input photon density in the resonator in the conventional example,
FIG. 6 is a diagram showing the relationship between optical output and optical input in a conventional example. 1o1... Semiconductor laser, 102...
Low reflectance film, 103... High reflectance film, 106.
...Light input, 106...Oscillation light, 109
...Polarizing beam splitter, 110...
- Faraday rotation element, 113...wavelength filter. Name of agent: Patent attorney Toshio Nakao and one other person lθ
One-handed conductor lede m-one low xi base film 103-one high anti-snoring half-narrow lθ4- electric 5 air source tOS--one optical input lθ6- speech light 107--activated counterfeit 10δ-optical isolator ut-- - Lens 112 - 11-light EkattS - 1-Yumi Hikari Flea Filter No. 2 Fig. 3 ρ/-- 1,400 Fubaku N Lep 3 θ 4 - Optical isolage 305 - 1-Optical Input Jc/1 Fig. 4 Optical Work or Ei Light Input direction

Claims (1)

[Claims] a semiconductor laser in which one end face has a low reflectance and the other end face has a high reflectance; a current source that supplies a bias current equal to or higher than a threshold current to the semiconductor laser; a means for unilaterally allowing light from the outside to enter; a means for selectively blocking laser light generated by the semiconductor laser among the light emitted from the end face having a low reflectance; and a means for selectively passing the light from the outside.