JPH04112589A - Optical control type optical frequency modulator - Google Patents

Abstract

PURPOSE:To attain optical control type high-performance optical frequency modulation, in which oscillation frequency is changed by light, by varying the refractive index of an inactive region. CONSTITUTION:Signal light IM(lambda1) having a wavelength lambda1 from an intensity- modulated light source 6 for excitation is projected and absorbed to an inactive region 2, and carriers are generated in response to the intensity of the incident light. The refractive index of the region 2 is altered by the plasma effect of the carriers, a Bragg wavelength is varied and oscillation frequency is changed, and frequency-modulated light FM(lambda2) is emitted. The wavelength lambda1 of incident light is made shorter than the absorption end wavelength of the optical guide layer of the region 2 so that incident light is absorbed efficiently only in the region 2 and an active region 3 is not subject to an effect at that time. Accordingly, an optical control type optical frequency modulator, which does not depend upon the direction of the polarized wave of incident light, can be acquired easily.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical frequency modulation device that generates frequency-modulated light used for optical fiber communication, optical measurement, and the like.

(Prior art) Optical frequency modulation (optical FSK) communication systems, optical sensors that use frequency-modulated light, and oscillation frequency control devices that control optical frequency according to error signals oscillate in a single mode. The optical frequency of the laser can be changed depending on the applied signal, a so-called modulation signal.

Methods for controlling optical frequency can be roughly divided into methods using injection current and methods using injection light. Semiconductor lasers belong to the former type, in which the oscillation optical frequency can be modulated by superimposing a modulation current on the injected current. In particular, distributed reflection semiconductor lasers (hereinafter referred to as
In DBR lasers) and distributed feedback semiconductor lasers (hereinafter referred to as DFB lasers), safe single-mode oscillation is possible even when frequency modulation is performed by injection current (e.g., IEEE Journal of Quantum
m Electronicsvol QE-23, No.
, 6 pp, 835-838.1987 S, Mura
ta et.

al,,' 5pectral Characteri
sticks for a 1.5μmDBRLa5er
with Frequency-Tuning Re
gion, 'see).

On the other hand, as an example of changing the oscillation wavelength by light, I
A report by Noue et al. (Electronics Le
ttersvo! , 25. No, 20pp, 136
0-1362.1989 K, Inoue 5ndN,
Takato+' Wavelength Conv
version for FM Ligtasing L
light Injection Induced Fr
sequence 5hiftin DFB-LD,'
), which is shown in Figure 6.

In FIG. 6, 21 is a DFB laser, 22 is an active region, 23 is an electrode for injecting current into the active region, and 24 is an excitation light source. In FIG. 6, the wavelength island light IM (λ
1) is incident, the incident light is absorbed, and the carrier concentration changes depending on its intensity, resulting in a change in the refractive index and a change in the oscillation frequency of the DFB laser. Light IM (λ2) of wavelength λ2 frequency-modulated in this manner is emitted. Here, in order to efficiently absorb the incident light, the wavelength λ1 of the incident light is set to be shorter than the absorption edge wavelength of the active layer of the active region.

(Problem to be Solved by the Invention) However, in the conventional example, unless the plane of polarization of the incident light to the DFB laser is perpendicular to the plane of polarization of the output light of the B laser, the incident light and the output light may combine with each other to make the oscillation state unstable, resulting in multimode oscillation.
In addition, frequency modulation with intensity modulation superimposed may become a factor that deteriorates transmission quality in optical communications.

The present invention has been made in view of these points, and its object is to provide an optically controlled high-performance optical frequency modulation device whose oscillation frequency is changed by light.

(Means for Solving the Problem) In order to achieve such an object, the present invention provides an integrated semiconductor laser comprising an active region that generates light and an inactive region that has low loss with respect to the oscillation wavelength. , an external signal light having a wavelength shorter than the absorption edge wavelength of the optical guide layer in the non-active region is incident on the non-active region, and is absorbed, changing the refractive index of the non-active region, thereby affecting the active region. The oscillation light frequency is changed without giving any

(Function) According to the present invention, light injected into the non-active region is absorbed by the light guide layer in the non-active region, and carriers are generated in the light guide layer in the non-active region. The effect of this carrier changes the refractive index of the inactive region, causing a change in the oscillation frequency. At this time, all of the injected light is absorbed in the non-active region, so it does not adversely affect the oscillation state of the active region and does not depend on the polarization direction of the incident light. Furthermore, in the inactive region, it is possible to increase the amount of change in carriers, which increases the amount of change in refractive index and also increases the amount of change in oscillation frequency.

Furthermore, by applying voltage or injecting current to the non-active region,
The oscillation frequency can be tuned, and optical frequency modulation can be performed while arbitrarily setting the oscillation frequency.

(Embodiment) FIG. 1 is a block diagram showing a first embodiment of an optically controlled optical frequency modulation device according to the present invention. In FIG. 1, 1 is a DBR laser, which includes an active region 3 that generates light by stimulated emission, a non-active region (distributed reflection region) 2 that wavelength-selectively reflects light by a diffraction grating, and an active region 3. It has an electrode 5 for injecting a current 1a, and an electrode 4 for applying a voltage or injecting a current to the non-active region 2.

Further, reference numeral 6 denotes a pumping light source (for example, a DF
B laser). In FIG. 1, intensity-modulated signal light IM (λI) of wavelength λ1 from excitation light source 6 is incident on inactive region 2 and absorbed, and carriers are generated according to the intensity of the incident light.

Due to the plasma effect of the generated carriers, the refractive index of the non-active region 2 changes, the Bragg wavelength changes, the oscillation frequency changes, frequency-modulated light FM (λ2) is emitted, and optically controlled light is generated. A frequency modulation device is realized. Here, the incident light is efficiently absorbed only in the non-active region 2,
In order not to affect the active region 3, the wavelength of the incident light λ,
is set to a wavelength shorter than the absorption edge wavelength of the optical guide layer in the non-active region 2.

Further, by injecting current or applying voltage to the non-active region 2 through the electrode 4, the oscillation frequency can be tuned.

FIG. 2 is a diagram showing the frequency change of the output light of the DBR laser when the intensity of the incident light is changed in the apparatus of FIG. 1. As is clear from FIG. 2, the oscillation frequency of the DBR laser can be changed by changing the intensity of the incident light.

FIG. 3 is a configuration diagram showing a second embodiment of the optically controlled optical frequency modulation device according to the present invention. The difference between this second embodiment and the first embodiment is that the non-active region 8 is divided into a distributed reflection region 8a containing a diffraction grating and a phase matching region 8b not containing a diffraction grating. The point is that it uses a laser. As described above, when using a BR laser and tuning the oscillation frequency by applying a voltage or injecting a current to the non-active region 8, the voltage applied to the distributed reflection region 8a and the phase matching region 8b or the injection current is applied to the non-active region 8. The oscillation frequency can be varied over a wide range by appropriately adjusting the current flowing through it (for example, Nikkei Electronics, 1987゜6, 15.
no, 423), I) p, 149-161, Kobayashi et al.
``Continuously changing the wavelength of the semiconductor laser'').

Note that in FIG. 3, the phase matching region 8b is arranged between the active region 3 and the distributed reflection region 8a, but even if it is provided on the right side of the active region 3, the same effect can be achieved by optically controlling the optical frequency. It is possible to configure a modulation device.

FIG. 4 is a configuration diagram showing a third embodiment of the optically controlled optical frequency modulation device according to the present invention. The difference between this third embodiment and the first embodiment is that the first embodiment uses a DBR laser, whereas the third embodiment uses a DFB laser with a phase matching region. It's because it's configured. In FIG. 4, reference numeral 11 denotes a DFB laser with a phase matching region, which includes an active region 12 that has a built-in diffraction grating and generates light by stimulated emission, and an inactive region (phase matching region) 1.
3, an electrode 15 for injecting current 1a into the active region, and an electrode 14 for applying voltage or injecting current to the non-active region. Even in such a configuration,
The change in oscillation frequency due to incident light can produce the same effects as in the first embodiment. Further, by injecting current or applying voltage to the non-active region 13 through the electrode 14, the oscillation frequency can be tuned.

Although there is only one electrode 15 in FIG. 4, the same result can be obtained even when a DFB with a phase matching region is used in which the electrode 15 is divided into a plurality of electrodes and the current 1a is non-uniformly injected into the active region. It is possible to construct an optically controlled optical frequency modulation device that is effective.

FIG. 5 is a block diagram showing a fourth embodiment of the present invention. In FIG. 5, 16 is the DB in the first embodiment.
This is an integrated optical control type optical frequency modulation device in which an R laser and an excitation light source (for example, a Kano B laser) are integrated on the same substrate, and includes a DBR laser section 1 and an excitation light source section 18. . Here, the excitation light source section 18 may be a Kano B laser or a light emitting diode. Electrode 2
A current on which a modulation signal is superimposed is injected into the active region 19 of the excitation light source section 18 through the DBR laser section 1, and intensity-modulated light having a wavelength shorter than the band edge wavelength of the active region 2 on the DBR laser section 1 is generated. . By absorbing the light in the non-active region, 7 frequency modulated light F on the DBR laser section 1 is generated.
It becomes possible to output M(λ,).

In addition, in FIG. 5, even if the DBR laser section 1 is replaced with a DBR laser with a phase matching region or a DFB laser with a phase matching region as in Example 2.3 above, the integrated optical control can have the same effect. It is possible to construct a type optical frequency modulation device.

(Effects of the Invention) As explained above, the optically controlled optical frequency modulator of the present invention has a tuning function of the oscillation wavelength, and facilitates the production of an optically controlled optical frequency modulator that does not depend on the polarization direction of incident light. can be obtained. Furthermore, since it does not depend on the polarization direction of the incident light, the above device can be easily constructed using optical fibers.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optically controlled optical frequency modulation device according to the present invention; FIG. 2 is a graph showing the amount of change in incident light intensity and oscillation frequency in the first embodiment; FIG. 3 is a configuration diagram showing a second embodiment of the optically controlled optical frequency modulator according to the present invention, and FIG. 4 is a configuration diagram showing a third embodiment of the optically controlled optical frequency modulator according to the present invention. Fig. 5 is a block diagram showing a fourth embodiment of the light-controlled optical frequency modulation device according to the present invention, and Fig. 6 is a block diagram of a conventional light-controlled optical frequency modulation device using a Kano B laser. It is. 1.7...DBR laser 2.8a...Distributed reflection region 3, 12.19.22...Active region 4, 5. 9.10.14.15.20.23...
Electrodes 6.24... Excitation light source 8b, 13... Phase matching region 11... Leaf B laser with phase matching region 16... Integrated optically controlled optical frequency modulator 17... DBR laser section 18... Excitation light source section 21... DFB laser.

Claims (1)

[Scope of Claims] 1. An integrated semiconductor laser composed of an active region that generates light and an inactive region that has low loss with respect to the oscillation wavelength; a light control type, characterized in that it is equipped with an excitation light source for inputting light with a wavelength shorter than the band edge wavelength of the region, and outputs frequency-modulated light from the active region side of the integrated semiconductor laser. Optical frequency modulator. 2. An integrated semiconductor laser consisting of an active region that generates light and a non-active region with low loss relative to the oscillation wavelength, and a light-emitting diode or semiconductor that emits light at a wavelength shorter than the band edge wavelength of the non-active region. 2. The optically controlled optical frequency modulator according to claim 1, wherein the laser is integrated on the same semiconductor substrate.