JPH0653616A - Semiconductor laser complete with wavelength sweep function - Google Patents

Abstract

PURPOSE:To conduct wideband wavelength sweep by using a semiconductor distribution reflector, as a laser reflector, which has regions repeatedly at a cycle of Mf (Mf>As, Ab) where a pitch of diffraction lattice on a optical waveguide path changes continuously or interruptedly from Aa to Ab. CONSTITUTION:This semiconductor laser is provided with a section 10a forming repeatedly, at a cycle of Mf, a region of a diffraction lattice where a pitch changes continuously from Aa to Ab, and a section 10b forming repeatedly, at a cycle of Mf, a region of a diffraction lattice where a pitch changes continuously from A'a to A'b. An active region 101 containing an active waveguide path layer 2, a distribution reflector regions 102 and 103 which have diffraction lattice-formed sections 10a and 10b, and a phase adjusting region 104 having a non-active waveguide path layer 3 where a diffraction lattice is not formed are electrically separated mutually. When the electric current flows into the active region 101, laser oscillation generates, and oscillating wavelength is changed by the distribution reflector regions 102, 103, and the phase adjusting region 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser having a wavelength sweeping function suitable as a light source for transmission, a tunable light source for synchronous detection, and a light source for optical measurement in an optical wavelength (frequency) multiplex communication system in the field of optical communication. It is about.

[0002]

2. Description of the Related Art In response to an increase in the amount of communication information in the future, research on an optical wavelength (frequency) multiplex communication system has been carried out. There is a demand for it, and also in the field of optical measurement, realization of a variable wavelength light source that covers a wide wavelength band is desired. As a variable wavelength light source, a number of distributed reflection type semiconductor lasers that can easily sweep the wavelength by injecting current have been studied. As an example of the realization of a distributed reflection type semiconductor laser with a wavelength function, a cross-sectional view of the structure is shown in FIG. 9 (for example, Electronics Letters Vol. 24, No. 24 by Tomori et al., 1).
481-1482, 1988). In FIG. 9, 2 is an active waveguide layer, 3 is an inactive waveguide layer, 20 is a diffraction grating, 101 is an active region, 102 and 103 are front and rear distributed reflector regions, and 104 is a phase adjustment region. Show.

[0003]

However, in the above conventional example, since the pitch of the diffraction grating 20 in the distributed reflector regions 102 and 103 is uniform, λ = 2Λn
The oscillation wavelength near the Bragg wavelength λ determined by _eq (Λ: pitch of diffraction grating, n _eq : equivalent refractive index) is an electrical equivalent refractive index change Δn _eq of the equivalent refractive index n _eq of the inactive waveguide region. It was decided. Therefore, the maximum refractive index change amount Δn / n of the semiconductor due to the normal current injection is about 1%, and thus the wavelength sweep width of the distributed reflection semiconductor laser of the conventional example is 100Å.
However, there is a problem that it is not sufficient as a light source for an optical wavelength division multiplexing communication system.

The object of the present invention is to solve the above-mentioned problems, and even if the equivalent refractive index change amount Δn _eq in the non-active waveguide region is about the same as the conventional one (about 1%), the gain bandwidth of the active waveguide region (about 10%).
It is to provide a semiconductor laser with a wavelength sweep function capable of sweeping a wide band wavelength over 00 Å).

[0005]

In order to solve this problem, in the optical waveguide including one or more optical waveguide layers formed on a semiconductor substrate and having an optical index larger than that of the semiconductor substrate, the optical waveguide Semiconductor distributed reflection in which a region in which the pitch of a diffraction grating formed on the road changes continuously or intermittently from Λ _a to Λ _b is repeatedly formed with _a period M _f (where M _f > Λ _a , Λ _b ). The device is used as a laser reflector.

As a laser structure, an active waveguide layer formed in a predetermined region on a semiconductor substrate and inactive waveguide layers optically coupled to the active waveguide layers before and after the active waveguide layer are formed. A distributed reflection semiconductor laser having a front and rear inactive waveguide regions partially or wholly composed of the above-mentioned semiconductor distributed reflector and formed in the front inactive waveguide region. The pitch of the diffraction grating is Λ _a
To Λ _b, regions that continuously or intermittently change are repeatedly formed with _a period M _f (where M _f > Λ _a , Λ _b ), and the diffraction grating formed in the non-active waveguide region on the rear side. Is a period M _r (where M _r > Λ _a ′, where P _r is continuously or intermittently changed from Λ _a ′ to Λ _b ′,
A semiconductor with a wavelength sweep function that is repeatedly formed with Λ _b ′) and that can control the refractive index of the front and rear inactive waveguide regions independently by current injection or voltage application to sweep the oscillation wavelength in a wide range. Use a laser.

Further, in the semiconductor laser with the wavelength sweep function, current injection or voltage application is performed in the non-active waveguide region where the diffraction grating is not formed,
A semiconductor laser with a wavelength sweep function that can sweep the oscillation wavelength over a wide range by controlling the refractive index in the above region is used.

Further, in the semiconductor laser having the wavelength sweep function, the semiconductor laser having the wavelength sweep function has two independent electrodes arranged in a comb shape above the inactive waveguide layer before and after the diffraction grating is formed. A semiconductor laser is used.

As another laser structure, a so-called multi-electrode distributed feedback having a diffraction grating above or below an active waveguide layer formed on a semiconductor substrate and having at least two or more electrically separated regions. Type semiconductor laser, a part or all of the active waveguide region is composed of the above-mentioned semiconductor distributed reflector, and the structure of the diffraction grating is different.
In the diffraction grating having two regions, the region in which the pitch changes continuously or intermittently from Λ _a to Λ _b has a period M _f (where M _f > Λ _a , Λ _b )
In the diffraction grating formed in the other region, the region in which the pitch changes continuously or intermittently from Λ _a ′ to Λ _b ′ has a period M _r (where M _r >
Λ _a ′, Λ _b ′) are repeatedly formed, and the refractive indexes of the two different active waveguide regions are controlled by independently injecting current, and the oscillation wavelength can be broadly swept while maintaining the laser oscillation state. A semiconductor laser with a sweep function is used.

Further, in the semiconductor laser having the wavelength sweep function, the refractive index of the region is controlled by changing the current value injected into the active waveguide region where the diffraction grating is not formed, thereby sweeping the oscillation wavelength in a wide range. A semiconductor laser with a wavelength sweeping function.

Further, in the semiconductor laser with the wavelength sweep function, two comb-shaped semiconductor lasers are provided above the active waveguide layers in two different regions where the diffraction grating is formed.
A semiconductor laser with wavelength sweep function that has two independent electrodes.

[0012]

The distributed reflector according to the first aspect of the present invention is shown in FIG.
As shown in, since the region in which the pitch of the diffraction grating changes continuously or intermittently from Λ _a to Λ _b is repeatedly formed with the period M _f , the reflection characteristic of the distributed reflector is
The wavelength interval Δλ _f = λ ₀ ² / 2n _eq M _f (λ ₀ = n _eq (Λ _a + Λ from the wavelength λ _a = 2Λ _a n _eq to the wavelength λ _b = 2Λ _b n _eq
b )) has the characteristic of having a reflection peak periodically. Therefore, as shown in FIG. 11, for convenience, the wavelengths of the reflection peak points are set to λ ₁ to λ _n . Here, in the semiconductor laser with a wavelength control function of the present invention, the distributed reflector (claims 2 to 4) and the distributed feedback type (claims 5 to 7) are different from the above-mentioned distributed reflector. Use one. The reflection characteristic of the other distributed reflector is set to the wavelength λ _a ′ = 2Λ _a ′ n.
_{From eq} to the wavelength λ _b ′ = 2n _eq Λ _b ′, the wavelength interval Δ
λ _r = λ ₀ ′ ² / 2n _eq M _r (λ ₀ ′ = n _eq (Λ _a ′ +
Λ _b ′)) has a characteristic that periodically has reflection peaks λ ₁ ′ to λ _k ′. Here, the pitch modulation periods M _f and M _r of the diffraction gratings of the two distributed reflection regions are formed with different periods.

In the second to fourth and fifth to seventh aspects, the refractive indices of the two different distributed reflection regions are controlled electrically independently of each other, and one wavelength λ _i (λ _{i of} λ ₁ to λ _n ( i =
₁ to n), _one of λ ₁ ′ to λ _k ′ can be tuned to cause laser oscillation only in the vicinity of λ _i . Figure 1
1 shows an example of oscillation of λ ₁ and λ ₂ , that is, i is 1 and 2. If λ _{1 to} λ _n and λ ₁ ′ to λ _k ′ are set to such an extent that the semiconductor gain band can be covered, the oscillation wavelength control that covers the gain band can be performed. Here, the above-mentioned diffraction grating is formed in an inactive region of a distributed Bragg reflector laser having inactive regions on both sides of the active region, and the resonator is composed only of the active region. According to claims 5 to 7, the above-mentioned diffraction grating is formed in the active region of the distributed feedback laser.

According to a third aspect of the present invention, the above-mentioned wavelength λ _i is controlled by controlling the refractive index of the phase adjusting region in which the diffraction grating is not formed in the non-active waveguide layer independently of the above-mentioned distributed reflection region. The oscillation wavelength can be finely adjusted in the vicinity, and therefore, laser oscillation can be performed in the entire wavelength band of λ _{1 to} λ ₂ .

Further, according to a sixth aspect of the present invention, the refractive index of the phase adjusting region in which the diffraction grating is not formed in the active region is controlled independently of the above distributed reflector region, so that the wavelength in the vicinity of the above wavelength λ _i is controlled. The oscillation wavelength can be finely adjusted. Therefore, laser oscillation can be performed in all wavelength bands in the entire range of λ _{1 to} λ ₂ .

In the distributed Bragg reflector semiconductor laser according to claim 4,
The average equivalent refractive index of the front and rear distributed reflectors is measured by independently injecting current or applying voltage to each one of the two sets of comb-shaped electrodes provided above the front and rear distributed reflectors. Laser oscillation can be obtained in the vicinity of the above-mentioned arbitrary wavelength λ _i by changing each independently. If the average refractive indices of the front and rear distributed reflectors are simultaneously changed by the same amount, fine adjustment of the oscillation wavelength in the vicinity of the wavelength λ _i becomes possible. In the distributed Bragg reflector semiconductor laser according to the present invention, the remaining two electrodes of the comb-shaped electrode are short-circuited and a current is injected or a voltage is applied to the electrodes to finely adjust the oscillation wavelength in the vicinity of λ _i. It can be carried out. Further, in the distributed Bragg reflector semiconductor laser according to the present invention, current is injected or voltage is simultaneously applied to the above-mentioned short-circuited comb-shaped electrode and the inactive waveguide region where the diffraction grating is not formed, so that the wavelength near λ _{i is} reached. The oscillation wavelength can be continuously swept with.

According to the distributed feedback semiconductor laser of the present invention, the current value injected into each one of the two sets of comb electrodes provided above the two distributed reflectors is changed. It is possible to independently change the average equivalent refractive index of the two distributed reflectors and obtain laser oscillation in the vicinity of the arbitrary wavelength λ _i described above. If the average refractive indices of the front and rear distributed reflectors are simultaneously changed by the same amount, fine adjustment of the oscillation wavelength in the vicinity of the wavelength λ _i becomes possible. In the distributed feedback semiconductor laser according to the present invention, the remaining two electrodes of the comb-shaped electrode are short-circuited and the current value injected into the electrodes is changed to finely adjust the oscillation wavelength in the vicinity of λ _i. be able to. Further, in the distributed feedback semiconductor laser according to the present invention, the current value injected into the above-mentioned short-circuited comb-shaped electrode and the active waveguide region in which the diffraction grating is not formed is changed at the same time, so that the wavelength near λ _i The oscillation wavelength can be continuously swept.

By the method described above, the wavelength λ
Laser oscillation can be obtained at any wavelength between ₁ and λ _n . Furthermore, the wavelengths λ _{1 to} λ _n and λ ₁ ′ to
If λ _k ′ is set to an extent that the gain band of the semiconductor can be covered, laser oscillation can be obtained at any wavelength within the above gain band.

[0019]

Embodiments [Embodiment 1] In Embodiments 1 and 2, claims 2, 3
The invention of

FIG. 1 shows an embodiment of a distributed reflection type semiconductor laser having a wavelength sweeping function according to the present invention. In FIG. 1, 1 is an n-type InP substrate and 2 is a bandgap wavelength of 1.55 μm.
m InGaAsP active waveguide layer, 3 is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm, 4
Is a p-type InP clad layer, 5 is a p (+)-type InGaAsP
Cap layer, 6 is p-type InP current blocking layer, 7 is n-type current blocking layer, 8 is n-type electrode, 9 is p-type electrode, and 10a
Is a portion in which a region of the diffraction grating whose pitch continuously changes from Λ _a to Λ _b is repeatedly formed with a period M _f , and 10b is a region of the diffraction grating whose pitch continuously changes from Λ _a ′ to Λ _b ′. _Are repeatedly formed with a period M _r , 11 is a coupling part of an active waveguide layer and an inactive waveguide layer, 101 is an active region, 102 and 103 are front and rear distributed reflector regions, and 104 is a phase. This is an adjustment area.

A method of manufacturing the distributed reflection laser with the wavelength sweeping function of the above embodiment will be briefly described. First, the n-type InP substrate 1 is formed by using the metalorganic vapor phase epitaxial growth method.
An active waveguide layer 2 and a non-active waveguide layer 3 are formed on top. After that, the resist applied on the surface of the inactive waveguide layer 3 is
The pattern of the diffraction grating whose pitch is modulated is transferred by the electron beam exposure method, and the diffraction gratings 10a and 10b are formed by etching using the transferred pattern as a mask. Then, the waveguide is processed into a stripe shape to control the transverse mode, and the p-type InP current block layer 6, the n-type current block layer 7, and the p-type InP clad layer 4 are again formed by using the metalorganic vapor phase epitaxial growth method. , And p (+)
The type InGaAsP cap layer 5 is sequentially manufactured. Then, the p-type electrode 9 and the n-type electrode 8 are formed, and further, the active region 101 including the active waveguide layer 2 and the distributed reflector region 102 having the diffraction grating formed portions 10a and 10b.
And 103, and the p-type electrode 9 and p (+) above their coupling part in order to electrically isolate the phase adjusting region 104 having the non-active waveguide layer in which the diffraction grating is not formed from each other. The InGaAsP cap layer 5 is removed.

In the diffraction grating of the distributed Bragg reflector semiconductor laser with wavelength sweeping function of this embodiment, in the portion 10a, a region in which the pitch continuously changes from 2459Å to 2389Å is repeatedly formed with a cycle of 75 μm, and 10b.
In the area, the region where the pitch continuously changes from 2454Å to 2385Å is repeatedly formed with a period of 67.5 μm.

In the distributed Bragg reflector semiconductor laser having the above-described structure, laser oscillation occurs when a current is passed through the active region 101, and currents are independently passed through the distributed reflector regions 102 and 103 and the phase adjustment region 104. , The oscillation wavelength is changed by applying a voltage. With a constant current flowing in the active region and no current flowing in the distributed reflector region 102 and the phase adjustment region 104, the distributed reflector region 1
FIG. 2 shows how the oscillation wavelength changes when the current of No. 03 is changed. As shown in FIG. 2, in the distributed Bragg reflector semiconductor laser of the present embodiment, the oscillation wavelength is changed from 1.575 μm to 1.53 by passing a current through the distributed reflector region 103.
A wavelength sweep of up to 450 Å can be obtained by changing every 50 Å up to 0 μm. Further, the oscillation wavelength can be changed over the entire range of 450 Å by controlling the currents flowing through the distributed reflector region 102 and the phase adjustment region 104, respectively.

In the above embodiment, the active waveguide layer,
Also, the case where the inactive waveguide layer is composed of a single semiconductor layer has been described, but the present invention can be applied to a structure in which a plurality of semiconductor layers having different compositions are laminated, such as a multiple quantum well structure. Is applicable.

[Embodiment 2] In Embodiment 1, the case where the pitch of the diffraction grating formed in the distributed reflector region changes continuously has been described. However, when the pitch of the diffraction grating changes intermittently. The present invention can also be applied to. Therefore, an example in which the pitch of the diffraction grating is intermittently changed will be described below. Structures other than the diffraction grating are
The diffraction grating 1 has the same structure as that of the first embodiment shown in FIG. 1 and is formed in the front distributed reflector region 102.
0a and the diffraction grating 10b formed in the rear distributed reflector region 103 have the following configuration. Diffraction grating 10a
Has a pitch of 7.5 μm from 2459 Å to 2389 Å
The region in which the pitch changes intermittently by 10 steps is formed with a repetition period of 75 μm, and the diffraction grating 10b has a repetition period of 67.5 μm in which the pitch changes intermittently in 9 steps by 7.5 μm from 2454 Å to 2385 Å. Is formed by. Table 1 shows the pitch of the diffraction grating used in this example and the Bragg wavelength when the control current is not injected.

[0026]

[Table 1]

Also in the semiconductor laser with the wavelength sweeping function having such a structure, the injection current value to each electrode is controlled by the method as described in the first embodiment, so that the value is increased from 1.575 μm to 1.530 μm. Of 450Å
The laser oscillation operation can be performed at all wavelengths within the range.

[Embodiment 3] Embodiments 3 and 4 show the inventions of claims 3 and 4.

FIG. 3 shows a structural diagram of an embodiment of a distributed Bragg reflector semiconductor laser with a wavelength sweeping function according to the present invention. In FIG. 3, (a) is a view of the distributed Bragg reflector semiconductor laser viewed from above, and (b) is a line AA ′ shown in (a).
FIG. 6 is a cross-sectional view of the distributed reflection type semiconductor laser taken along with, and (c) is a cross-sectional view of the distributed reflection semiconductor laser taken along line BB ′ shown in (a). In FIG. 3, 1 is an n-type InP substrate, 2 is an InGaAsP active waveguide layer having a bandgap wavelength of 1.55 μm, 3 is an InGaAsP inactive waveguide layer having a bandgap wavelength of 1.3 μm, and 4 is a p-type InP clad. Layer 5 is p (+) type I
nGaAsP cap layer, 6 is a p-type InP current blocking layer, 7 is an n-type current blocking layer, 8 is an n-type electrode, 9a is a p-type electrode provided in the active region 101, and 9b is provided in the phase adjustment region 104. p-type electrodes, 9c and 9d are a pair of comb-type p-type electrodes provided in the front distributed reflector region 102,
9e and 9f are a pair of p-type p-type electrodes provided in the distributed reflector region 103 on the rear side, and 10a is a region of a diffraction grating whose pitch continuously changes from Λ _a to Λ _b and is repeated with a period M _f . The formed portion 10b is a portion in which a region of the diffraction grating whose pitch continuously changes from Λ _a ′ to Λ _b ′ is repeatedly formed with a period M _r , and 11 is an active waveguide layer and an inactive waveguide layer. It is the connecting part.

In the diffraction grating of the distributed Bragg reflector semiconductor laser with wavelength sweeping function of this embodiment, in the portion 10a, a region in which the pitch continuously changes from 2459Å to 2389Å is repeatedly formed with a period of 75 μm, and 10b.
In the area, the region where the pitch continuously changes from 2454Å to 2385Å is repeatedly formed with a period of 67.5 μm. Further, in the comb-shaped electrode, the repetition cycle of the individual electrodes that are finely divided into a comb shape is the same as the pitch modulation cycle of the diffraction grating. That is, the individual electrodes of the comb-shaped electrodes 9c and 9d in the front distributed reflector region are 75 μm.
The electrodes are repeatedly formed in a cycle, and the length of the electrode is almost half the cycle. The individual electrodes of the comb-shaped electrodes 9e and 9f in the rear distributed reflector region are 67.5.
It is repeatedly formed with a period of μm.

In the distributed Bragg reflector semiconductor laser having the above-described structure, laser oscillation occurs when a current is passed through the active region 101, and a current is independently passed through the distributed reflector regions 102 and 103 and the phase adjustment region 104. , The oscillation wavelength is changed by applying a voltage.

A constant current is applied to the active region, and 9c, 9d, and 9f of the comb-shaped electrodes provided in the front and rear distributed reflector regions 102 and 103 and the p-type electrode 9b provided in the phase adjustment region 104. FIG. 4 shows how the oscillation wavelength changes when the current flowing through the comb-shaped electrode 9e provided in the distributed reflector region 103 is changed while no current is flowing. As shown in FIG. 4, in the distributed Bragg reflector semiconductor laser of the present embodiment, by passing a current through the distributed reflector region 103,
Oscillation wavelength from 1.575μm to 1.530μm about 5
It can be changed every 0Å.

Further, in the above-mentioned state, the value of the current flowing through the comb-shaped electrodes 9c and 9e is fixed, and one of the oscillation wavelengths that changes at intervals of about 50 Å is selected. It is possible to finely adjust the oscillation wavelength by electrically shorting 9f and injecting a current into the electrodes at the same time. The solid line in FIG. 5 shows how the oscillation wavelength changes when the current flowing through the short-circuited comb electrodes 9d and 9f is changed. As shown in FIG. 5, in the distributed Bragg reflector semiconductor laser of the present embodiment, the oscillation wavelength can be changed by about 50 Å while causing the wavelength jump by causing a current to flow through the shorted comb electrodes 9d and 9f at the same time. .

Further, p provided in the phase adjustment region 104
An electric current is applied to the mold electrode 9b to short-circuit the comb electrodes 9d and 9d.
A change in the oscillation wavelength when the currents flowing through f and f is changed is shown by a broken line in FIG. In this way, by controlling the current flowing through the p-type electrode 9b provided in the phase adjustment region, the oscillation wavelength can be further finely adjusted.

By adjusting the currents flowing through the p-type electrodes 9b to 9f by the procedure described above, rough adjustment of the oscillation wavelength,
By fine adjustment, it becomes possible to select an arbitrary oscillation wavelength over the wavelength range of 450Å.

[Embodiment 4] In Embodiment 3, the case where the pitch of the diffraction grating formed in the distributed reflector region changes continuously has been described. However, when the pitch of the diffraction grating changes intermittently. The present invention can also be applied to. Therefore, an example in which the pitch of the diffraction grating is intermittently changed will be described below. Structures other than the diffraction grating are
The diffraction grating 1 has the same structure as that of the third embodiment shown in FIG. 3 and is formed in the front distributed reflector region 102.
0a and the diffraction grating 10b formed in the rear distributed reflector region 103 have the following configuration. Diffraction grating 10a
Has a pitch of 7.5 μm from 2459 Å to 2389 Å
The region in which the pitch changes intermittently by 10 steps is formed with a repetition period of 75 μm, and the diffraction grating 10b has a repetition period of 67.5 μm in which the pitch changes intermittently in 9 steps by 7.5 μm from 2454 Å to 2385 Å. Is formed by. Table 1 shows the pitch of the diffraction grating used in this example and the Bragg wavelength when the control current is not injected.

Also in the distributed reflection type semiconductor laser having the wavelength sweeping function having such a structure, the injection current value to each electrode is controlled by the method as described in the third embodiment, so that the value from 1.575 μm to 1 can be obtained. Laser oscillation can be performed at all wavelengths within the range of 450 Å up to 0.530 μm.

[Embodiment 5] Embodiment 5 shows the invention of claim 4.

In the third and fourth embodiments, the pitch modulation period of the diffraction grating and the repetition period of the individual electrodes of the comb-shaped electrode are the same, but the repetition period of the individual electrodes of the comb-shaped electrode is the same as that of the diffraction grating. When it is smaller than the pitch modulation period, the same effect as that of the above-mentioned embodiment can be obtained. On the other hand, if the electrode repetition period is longer than the pitch modulation period of the diffraction grating, a different effect is obtained. As an example thereof, the structure other than the distributed reflection type semiconductor laser with wavelength sweeping function of the third embodiment shown in FIG. 3 and the comb-shaped electrodes are all the same, and the length of each of the comb-shaped electrodes 9c to f is doubled. A method of controlling the oscillation wavelength of the semiconductor laser having the above structure will be described below.

FIG. 6 shows the reflection characteristics of the distributed reflector region of the semiconductor laser in this embodiment. When no current is injected into the comb-shaped electrode, as shown in FIG. 6A, the reflection characteristic has periodic reflection peaks at a wavelength interval Δλ _f corresponding to the pitch modulation period M _f of the diffraction grating. Here, when a current is injected into one electrode of a pair of comb-shaped electrodes in which individual electrodes are repeatedly formed at a period of 2M _f provided above the diffraction grating, the refractive index changes at a period of 2M _f . In order to
As shown in (b), the characteristics have periodic reflection peaks at the wavelength interval Δλ _f / 2. Further, when the amount of current flowing through the electrode is increased, the reflection characteristic when no current is passed is shifted by Δλ _f / 2, as shown in FIG. 6C. By using the principle as described above, it is possible to roughly adjust the oscillation wavelength at the wavelength interval Δλ _f / 2. That is, in the semiconductor lasers of Examples 1 and 2, the oscillation wavelength can be roughly adjusted every 50Å, whereas in the semiconductor laser of this example, the oscillation wavelength can be roughly adjusted every 25Å.

[Embodiment 6] Embodiments 6 and 7 show the invention of claim 5.

FIG. 7 shows a structural diagram of one embodiment of a distributed feedback type semiconductor laser with a wavelength sweeping function. Figure 7
1, 1 is an n-type InP substrate, 2 is an InGaAsP active layer having a bandgap wavelength of 1.55 μm, 3 is an InGaAsP optical confinement layer having a bandgap wavelength of 1.3 μm, 4 is a p-type InP clad layer, and 5 is p ( +) Type InGa
AsP cap layer, 6 is p-type InP current blocking layer, 7
Is an n-type current blocking layer, 8 is an n-type electrode, 9 is a p-type electrode,
Reference numeral 10a denotes a portion in which a region of the diffraction grating whose pitch continuously changes from Λ _a to Λ _b is repeatedly formed with a period M _f.
b is a portion where a region of the diffraction grating whose pitch continuously changes from Λ _a ′ to Λ _b ′ is repeatedly formed with a period M _r , 10
Reference numerals 2 and 103 are front and rear distributed reflector regions, and 104 is a phase adjustment region.

A method of manufacturing the semiconductor laser with the wavelength sweeping function of the above embodiment will be briefly described. First, the active layer 2 and the optical confinement layer 3 are formed on the n-type InP substrate by using the metalorganic vapor phase epitaxial growth method. After that, the pattern of the pitch-modulated diffraction grating is transferred to the resist applied on the surface of the light confinement layer 3 by the electron beam exposure method, and the transfer patterns are used as masks to form the diffraction gratings 10a and 10b by etching. . And
By processing the waveguide in a stripe shape to control the transverse mode, and again using the metalorganic vapor phase epitaxial growth method,
p-type InP current blocking layer 6, n-type current blocking layer 7,
p-type InP clad layer 4 and p (+)-type InGaAsP
The cap layer 5 is sequentially manufactured. After that, the p-type electrode 9 and the n-type electrode 8 are formed, and further the distributed reflector regions 102 and 103 having the portions 10a and 10b in which the diffraction grating is formed, and the inactive waveguide layer in which the diffraction grating is not formed. In order to electrically isolate the phase adjusting regions 104 having the above-mentioned characteristics from each other, the p-type electrode 9 and the p (+)-type InGaAsP cap layer 5 above their coupling portion are removed.

In the diffraction grating of the semiconductor laser with wavelength sweeping function of this embodiment, the pitch is 24 in the portion 10a.
Regions that continuously change from 59 Å to 2389 Å are repeatedly formed at a period of 75 μm, and in the portion 10b, regions where the pitch continuously changes from 2454 Å to 2385 Å are repeatedly formed at a period of 67.5 μm.

In the semiconductor laser with the wavelength sweeping function having the above-mentioned configuration, laser oscillation occurs by injecting current into the entire region, and the current values in the distributed reflector regions 102 and 103 and the phase adjustment region 104 are independently set. The oscillation wavelength is changed by changing it. Front distributed reflector area 1
02 and the phase adjustment region 104 with a constant current flowing,
FIG. 2 shows how the oscillation wavelength changes when the current in the rear distributed reflector region 103 is changed. As shown in FIG.
In the semiconductor laser of the present embodiment, when the current is passed through the distributed reflector region 103, the oscillation wavelength changes from 1.575 μm to 1.530 μm at intervals of about 50 Å, and the maximum is 45.
A wavelength sweep of 0Å is obtained. Further, the distributed reflector region 1
The oscillation wavelength can be changed over the entire range of 450 Å by controlling the currents flowing in 02 and the phase adjustment region 104, respectively.

In the above-described embodiments, the case where the active layer is composed of a single semiconductor layer has been described. However, a so-called multiple quantum well structure in which semiconductor layers having different compositions are alternately stacked is used as the active layer. The present invention is applicable even when provided.

[Embodiment 7] In Embodiment 6, the case where the pitch of the diffraction grating formed in the distributed reflector region changes continuously has been described. However, when the pitch of the diffraction grating changes intermittently. The present invention can also be applied to. Therefore, an example in which the pitch of the diffraction grating is intermittently changed will be described below. Structures other than the diffraction grating are
The diffraction grating 1 has the same structure as that of the sixth embodiment shown in FIG. 7 and is formed in the front distributed reflector region 102.
0a and the diffraction grating 10b formed in the rear distributed reflector region 103 have the following configuration. Diffraction grating 10a
Has a pitch of 7.5 μm from 2459 Å to 2389 Å
The region in which the pitch changes intermittently by 10 steps is formed with a repetition period of 75 μm, and the diffraction grating 10b has a repetition period of 67.5 μm in which the pitch changes intermittently in 9 steps by 7.5 μm from 2454 Å to 2385 Å. Is formed by. Table 1 shows the pitch of the diffraction grating used in this example and the Bragg wavelength when the control current is not injected.

Also in the semiconductor laser having the wavelength sweeping function having such a structure, the injection current value to each electrode is controlled by the method as described in the first embodiment, so that the value is increased from 1.575 μm to 1.530 μm. Of 450Å
The laser oscillation operation can be performed at all wavelengths within the range.

[Embodiment 8] Embodiments 8 and 9 are claims 6 and 7.
The invention of

FIG. 8 shows a structural diagram of an embodiment of a semiconductor laser having a wavelength sweep function according to the present invention. In FIG.
(A) is a view of the semiconductor laser as viewed from above,
(B) is a cross-sectional view of the semiconductor laser taken along line AA 'shown in (a), and (c) is a semiconductor laser taken along line BB' shown in (a). FIG. In FIG. 8, 1 is an n-type InP substrate, 2 is an InGaAsP active layer having a bandgap wavelength of 1.55 μm,
3 is InGaAsP having a band gap wavelength of 1.3 μm
Optical confinement layer, 4 is p-type InP clad layer, 5 is p (+)
Type InGaAsP cap layer, 6 is a p type InP current blocking layer, 7 is an n type current blocking layer, 8 is an n type electrode, 9
c and 9d are 1 provided in the front distributed reflector region 102.
A pair of comb-type p-type electrodes, 9e and 9f are a pair of comb-type p-type electrodes provided in the rear distributed reflector region 103, 9b is a p-type electrode provided in the phase adjustment region 104, and 10a is a pitch Is a portion in which a region of the diffraction grating in which is continuously changed from Λ _a to Λ _b is repeatedly formed with a period M _f , and 10b has a pitch Λ _a ′.
The region of the diffraction grating that continuously changes from to Λ _b ′ is a portion repeatedly formed with the period M _r .

In the diffraction grating of the semiconductor laser with wavelength sweeping function of this embodiment, the pitch is 24 in the portion 10a.
Regions that continuously change from 59 Å to 2389 Å are repeatedly formed at a period of 75 μm, and in the portion 10b, regions where the pitch continuously changes from 2454 Å to 2385 Å are repeatedly formed at a period of 67.5 μm.

In the semiconductor laser having the above-described structure, laser oscillation occurs when a current is appropriately applied to all regions, and the distributed reflector regions 102 and 103 and the phase adjusting region 1 are generated.
The oscillation wavelength is changed by individually passing currents to 04.

A constant current is caused to flow through 9c, 9d, and 9f of the comb-shaped electrodes provided in the front and rear distributed reflector regions 102 and 103 and the p-type electrode 9b provided in the phase adjustment region 104 to cause laser oscillation. FIG. 4 shows how the oscillation wavelength changes when the current flowing through the comb-shaped electrode 9e provided in the distributed reflector region 103 is changed in the state in which the light is generated. As shown in FIG. 4, in the semiconductor laser of this embodiment, the comb-shaped electrode 9
The oscillation wavelength can be changed from 1.575 μm to 1.530 μm at intervals of about 50 Å by changing the value of the current flowing through e.

Further, in the above-mentioned state, the value of the current flowing through the comb-shaped electrode 9e is fixed, and one of the oscillation wavelengths that changes at intervals of about 50 Å is selected. It is possible to finely adjust the oscillation wavelength by electrically short-circuiting and changing the value of the current flowing through the electrodes at the same time. FIG. 5 shows how the oscillation wavelength changes when the current flowing through the short-circuited comb electrodes 9d and 9f is changed.
Is indicated by a solid line. As shown in FIG. 5, in the semiconductor laser of the present embodiment, the oscillation wavelength can be changed by about 50Å while causing the wavelength jump by causing the current to flow through the short-circuited comb electrodes 9d and 9f at the same time.

Furthermore, the state of change in the oscillation wavelength when the current flowing through the p-type electrode 9b provided in the phase adjustment region 104 is changed to change the current flowing through the shorted comb electrodes 9d and 9f. It is indicated by a broken line in FIG. In this way, by controlling the current flowing through the p-type electrode 9b provided in the phase adjustment region, the oscillation wavelength can be further finely adjusted.

By adjusting the current flowing through the p-type electrodes 9b to 9f according to the procedure described above, rough adjustment of the oscillation wavelength,
By fine adjustment, it becomes possible to select an arbitrary oscillation wavelength over the wavelength range of 450Å.

[Embodiment 9] In Embodiment 8, the case where the pitch of the diffraction grating formed in the distributed reflector region changes continuously has been described. However, in the case where the pitch of the diffraction grating changes intermittently. The present invention can also be applied to. Therefore, an example in which the pitch of the diffraction grating is intermittently changed will be described below. Structures other than the diffraction grating are
The diffraction grating 1 having the same structure as that of the eighth embodiment shown in FIG. 8 and formed in the front distributed reflector region 102
0a and the diffraction grating 10b formed in the rear distributed reflector region 103 have the following configuration. Diffraction grating 10a
Has a pitch of 7.5 μm from 2459 Å to 2389 Å
The region in which the pitch changes intermittently by 10 steps is formed with a repetition period of 75 μm, and the diffraction grating 10b has a repetition period of 67.5 μm in which the pitch changes intermittently in 9 steps by 7.5 μm from 2454 Å to 2385 Å. Is formed by. Table 1 shows the pitch of the diffraction grating used in this example and the Bragg wavelength when the control current is not injected.

Also in the semiconductor laser with the wavelength sweeping function having such a structure, the injection current value to each electrode is controlled by the method as described in the eighth embodiment, so that the current from 1.575 μm to 1.530 μm can be obtained. Of 450Å
Laser oscillation can be performed at all wavelengths within the range.

[Embodiment 10] Embodiment 10 shows the invention of claim 7.

In the embodiment, the case where the pitch modulation period of the diffraction grating and the repetition period of the individual electrodes of the comb-shaped electrode are the same is explained. However, the repetition period of the individual electrodes of the comb-shaped electrode is the pitch modulation period of the diffraction grating. If it is smaller than the above, the same effect as that of the above embodiment can be obtained. On the other hand, if the electrode repetition period is longer than the pitch modulation period of the diffraction grating, a different effect is obtained. As an example, the semiconductor laser with wavelength sweeping function of the eighth embodiment shown in FIG. 8 and the structure other than the comb-shaped electrode are all the same, and the length of each of the comb-shaped electrodes 9c to 9f is doubled. The laser diode
The method of controlling the oscillation wavelength will be described below.

FIG. 6 shows the reflection characteristics of the distributed reflector region of the semiconductor laser in this embodiment. When no current is injected into the comb-shaped electrode, as shown in FIG. 6A, the reflection characteristic has periodic reflection peaks at the wavelength interval Δλ _f corresponding to the pitch modulation period M _f of the diffraction grating. Here, when a current is injected into one electrode of a pair of comb-shaped electrodes in which individual electrodes are repeatedly formed at a period of 2M _f provided above the diffraction grating, the refractive index changes at a period of 2M _f . Therefore, as shown in FIG. 6 (b), the characteristic is such that the reflection peaks are periodically reflected at the wavelength interval Δλ _f / 2. Further, when the amount of current flowing through the electrode is increased, the reflection characteristic when no current is passed is shifted by Δλ _f / 2, as shown in FIG. 6C. By using the principle as described above, it is possible to roughly adjust the oscillation wavelength at the wavelength interval Δλ _f / 2. That is,
In the semiconductor lasers of Examples 1 and 2, the oscillation wavelength can be roughly adjusted every 50Å, whereas in the semiconductor laser of this example, the oscillation wavelength can be roughly adjusted every 25Å.

[0062]

As described above, in the semiconductor laser with wavelength sweeping function according to the present invention, the optical waveguide layer formed on the semiconductor substrate and having an optical index larger than that of the semiconductor substrate is
In a semiconductor distributed reflector having an optical waveguide including more than one layer, the pitch of the diffraction grating formed on the optical waveguide is Λ
_The region that changes continuously or intermittently from _a to Λ _b is
By using the semiconductor distributed reflector that is repeatedly formed with the period M _f (where M _f > Λ _a , Λ _b ), wideband wavelength sweeping can be performed with good controllability over the gain bandwidth of the active waveguide layer. A semiconductor laser with a wavelength sweep function can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic structural diagram of an embodiment of a distributed Bragg reflector semiconductor laser with a wavelength sweeping function according to the present invention.

FIG. 2 is a diagram showing how the oscillation wavelength changes in one embodiment of the distributed Bragg reflector semiconductor laser according to the present invention.

3A and 3B are structural views showing an embodiment of a distributed reflection type semiconductor laser with a wavelength control function according to the present invention, wherein FIG. 3A is a plan view of the semiconductor laser, and FIG. 3B is AA ′ shown in the plan view.
A sectional view, (c) is a BB 'sectional view shown in the above plan view.

FIG. 4 is a diagram showing how the oscillation wavelength is roughly adjusted in the distributed Bragg reflector semiconductor laser of the present invention.

FIG. 5 is a diagram showing how the oscillation wavelength of the distributed Bragg reflector semiconductor laser is finely adjusted.

FIG. 6 is a diagram showing the reflection characteristics of the distributed reflector region of the distributed Bragg reflector semiconductor laser according to the embodiment of the present invention, where (a) shows a case where no current is injected into the comb electrodes, and (b) shows one set. When a current is injected into one of the comb-shaped electrodes, (c) is a diagram showing a case where the current supplied to the electrode is increased.

FIG. 7 is a schematic structural diagram showing an embodiment of a semiconductor laser with a wavelength sweep function according to the present invention.

8A and 8B are structural views showing an embodiment of a semiconductor laser having a wavelength sweeping function according to the present invention, FIG. 8A is a plan view of the semiconductor laser, and FIG. 8B is a sectional view taken along the line AA ′ shown in the plan view.
(C) is a BB 'sectional view shown in the above plan view.

FIG. 9 is a sectional view of a conventional distributed Bragg reflector laser.

FIG. 10 is a conceptual diagram of a diffraction grating formed in a distributed Bragg reflector region of a distributed Bragg reflector semiconductor laser with a wavelength sweeping function of the present invention, where (a) is a continuous grating and (b) is a stepwise interrupted pattern. It is a figure which shows the case where it was formed in a desired manner.

FIG. 11 is a diagram showing a method of setting an oscillation wavelength by the distributed Bragg reflector semiconductor laser of the present invention, in which (a) is a reflection peak wavelength diagram of a front distributed reflector region, and (b) is a reflection of a rear distributed reflector region. Peak wavelength diagram, (c) λ ₁ oscillation example, (d) λ ₂
Examples of oscillation are shown below.

[Explanation of symbols]

 1 semiconductor substrate 2 optical waveguide layer 3 inactive waveguide layer 9c, 9d, 9e, 9f comb-shaped electrodes 10a, 10b diffraction grating 101 active waveguide region 102, 103 inactive waveguide region 104 phase adjustment region

Claims (7)

[Claims] 1. A semiconductor distributed reflector having an optical waveguide including one or more optical waveguide layers having an optical index higher than that of the semiconductor substrate formed on the semiconductor substrate, the semiconductor distributed reflector being formed on the optical waveguide. The diffraction grating pitch is Λ _a to Λ _b
The region that continuously or intermittently changes to the period M _f
(However, M _f > Λ _a , Λ _b ) The semiconductor distributed reflector is characterized by being repeatedly formed. 2. A distribution having an active waveguide layer formed in a predetermined region on a semiconductor substrate, and a non-active waveguide layer optically coupled to the active waveguide layer before and after the active waveguide layer. It is a reflection type semiconductor laser, Comprising: A part or all of said front and back non-active waveguide area | regions is comprised by the semiconductor distributed reflector of Claim 1, Comprising: It forms in the front side non-active waveguide area | region. In the diffraction grating described above, a region in which the pitch changes continuously or intermittently from Λ _a to Λ _b is repeatedly formed with _a period M _f (where M _f > Λ _a , Λ _b ), and the rear side non- In the diffraction grating formed in the active waveguide region, a region in which the pitch changes continuously or intermittently from Λ _a ′ to Λ _b ′ has a period M _r (where M _r > Λ _a ′, Λ _b ′). The refractive index of the front and rear inactive waveguide regions, which are repeatedly formed, are respectively Controlled by performing the independent current injection or voltage application, the wavelength sweep function semiconductor laser, characterized by sweeping the oscillation wavelength. 3. The semiconductor laser with wavelength sweeping function according to claim 2, wherein current is injected or voltage is applied to the non-active waveguide region where no diffraction grating is formed to refract the non-active waveguide region. A semiconductor laser with a wavelength sweep function, characterized in that the oscillation wavelength is swept by controlling the rate. 4. The semiconductor laser with wavelength sweeping function according to claim 2, wherein two independent electrodes arranged in a comb shape are provided above the inactive waveguide layer before and after the diffraction grating is formed. A semiconductor laser having a wavelength sweeping function, which has. 5. A so-called multi-electrode distributed feedback semiconductor laser having a diffraction grating above or below an active waveguide layer formed on a semiconductor substrate and having at least two electrically separated regions, A part or all of the active waveguide region is composed of the semiconductor distributed reflector according to claim 1, and has two regions having different diffraction grating configurations, and the diffraction formed in one region of the two regions. In the lattice, a region in which the pitch continuously or intermittently changes from Λ _a to Λ _b is repeatedly formed with _a period M _f (where M _f > Λ _a , Λ _b ) and is formed in the other region. In the diffraction grating, a region in which the pitch continuously or intermittently changes from Λ _a ′ to Λ _b ′ is repeatedly formed with _a period _Mr (where M _r > Λ _a ′, Λ _b ′), which is different from the above. The refractive indices of the two active waveguide regions Controls performed current injection respectively independently,
A semiconductor laser with a wavelength sweep function, which sweeps the oscillation wavelength while maintaining the laser oscillation state. 6. The semiconductor laser with wavelength sweeping function according to claim 5, wherein the refractive index of the active waveguide region is changed by changing the current value injected into the active waveguide region in which the diffraction grating is not formed. A semiconductor laser with a wavelength sweep function, which is controlled to sweep the oscillation wavelength. 7. The semiconductor laser with wavelength sweeping function according to claim 5, wherein a different diffraction grating is formed.
A semiconductor laser with a wavelength sweeping function, comprising two independent electrodes arranged in a comb shape above the active waveguide layer in one region.