JPH0832163A - Variable-wavelength semiconductor light emitting device - Google Patents

Abstract

PURPOSE:To obtain a highly reliable variable-wavelength semiconductor light emitting device the emission wavelength of which can be swept at a high speed without driving the device mechanically. CONSTITUTION:A light beam 11 emitted from the end face 10b of a semiconductor optical amplifier 10 is diffracted by a prescribed angle of diffraction through an AOM 13 and the diffracted beam 11 is reflected by a mirror 14 so as to return the beam 11 to the amplifier 10. In addition, a variable-frequency high-frequency signal RF is impressed upon the AOM 13 from an AOM modulation driver 15.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device,
Particularly in detail, a semiconductor optical amplifier is used as a light emitting source, and the wavelength of light emitted from the semiconductor optical amplifier is selected within a certain range and returned to the semiconductor optical amplifier so that the emission wavelength can be changed. The present invention relates to a semiconductor light emitting device.

[0002]

2. Description of the Related Art Conventionally, various attempts have been made to obtain a wavelength tunable light beam using a semiconductor. ELECTRONICS
LETTERS (Electronics Letters) Vol.29, N
One of such wavelength tunable semiconductor light emitting devices is shown in O.14, (1993) pp.1254-1255.

As shown in FIG. 2, this semiconductor light emitting device has a semiconductor optical amplifier 1 as a light emitting source. The light emitted from a rear end face 1a of the semiconductor optical amplifier 1 is collimated by a lens 2 and then reflected. The light is reflected by the type diffraction grating 3 and returned to the semiconductor optical amplifier 1. In this configuration, the light 4 whose wavelength is selected by the diffraction grating 3 is returned to the semiconductor optical amplifier 1 so that its front end face 1
The wavelength of the light 4F emitted from b is locked to a single wavelength,
When the installation angle is changed so that the light incident angle on the diffraction grating 3 is changed, the emission wavelength is changed.

[0004]

By the way, the wavelength tunable semiconductor light emitting device as described above may be used in applications where it is necessary to sweep the emission wavelength, such as a light source for optical heterodyne measurement. In that case, the diffraction grating 3 is mechanically driven so that its installation angle changes, but it is difficult to perform such mechanical driving at high speed, and therefore,
It is difficult to sweep the emission wavelength at high speed.

Further, the wavelength tunable semiconductor light emitting device which is mechanically driven as described above is also difficult in terms of reliability.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a highly reliable wavelength tunable semiconductor light emitting device capable of sweeping the emission wavelength at high speed without mechanical driving. It is intended.

[0007]

A wavelength tunable semiconductor light emitting device according to the present invention includes a semiconductor optical amplifier, an acousto-optical element for diffracting light emitted from one end surface of the semiconductor optical amplifier, and a predetermined optical acousto-optical element. It is characterized by comprising a mirror for reflecting the light diffracted at the diffraction angle so as to return to the original optical path and a driver for applying a frequency-variable high frequency signal to the acoustooptic device.

[0008]

In the above structure, the grating spacing of the diffraction grating formed in the acousto-optic element is d, the predetermined diffraction angle in the acousto-optic element is 90 ° -θ (θ is the Bragg angle), and the acousto-optic Assuming that the refractive index of the ultrasonic medium of the device is n and the emission wavelength is λ, 2d sin θ = nλ, and therefore λ = (2d sin θ) / n.

Since the mirror is arranged as described above, only the light diffracted at the predetermined diffraction angle can return to the one end face of the semiconductor optical amplifier, and the emission wavelength is locked. In other words, the diffraction angle is fixed for the light that returns to the semiconductor optical amplifier and locks its emission wavelength. Further, since the refractive index n is also fixed, if the frequency (carrier frequency) of the high frequency signal applied to the acousto-optic element is changed to change the lattice spacing d, the emission wavelength λ is uniquely changed according to the value of d. Will be done.

Therefore, when the frequency of the high frequency signal is swept, the emission wavelength λ is swept. This frequency sweep can be done fast enough, unlike mechanical drive,
The emission wavelength λ can be swept sufficiently fast.

Further, as described above, the wavelength tunable semiconductor light emitting device of the present invention has a high reliability because it can sweep the emission wavelength by electric operation and does not require any mechanical driving. Can be.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on the embodiments shown in the drawings. FIG. 1 shows a wavelength tunable semiconductor light emitting device according to an embodiment of the present invention. As shown, this wavelength tunable semiconductor light emitting device has a taper stripe 10
a semiconductor optical amplifier 10 having a, and this semiconductor optical amplifier 10
Collimator lens 12 for collimating the light beam 11 emitted from the rear end face 10b of the
AOM (acousto-optic light modulator) 13 that diffracts
A mirror 14 for reflecting the light beam 11 diffracted at a predetermined diffraction angle in the OM 13 back to the original optical path;
High frequency signal R with variable frequency to the transducer 13a of 13
It is composed of an AOM modulation driver 15 for applying F.

The semiconductor optical amplifier 10 is, for example, an n-GaAs substrate (Si = 2 × 10 ¹⁸ cm ⁻³ doped) with n.
-GaAs buffer layer (Si = 1 × 10 ¹⁸ cm ^-3 doped,
Layer thickness 0.5 μm), n-Al _0.5 Ga _0.5 As clad layer (Si = 1 × 10 ¹⁸ cm ⁻³ doped, layer thickness 2.5 μm), n−
Al _0.25 Ga _0.75 As optical guide layer (undoped, layer thickness of 0.
05 μm), n-Al _0.05 Ga _0.95 As quantum well layer (undoped, layer thickness 8 nm), n-Al _0.25 Ga _0.75 As optical guide layer (undoped, layer thickness 0.05 μm), p-Al _0.5 G
a _0.5 As clad layer (Zn = 1 × 10 ¹⁸ cm ⁻³ doped,
Layer thickness 2 μm, p-GaAs cap layer (Zn = 5 × 10 5
^{An 18} cm ⁻³ doped layer having a layer thickness of 0.3 μm) formed by a low pressure MOCVD method can be used.

Further, the taper stripe 10a is formed of, for example, SiO on the cap layer by a plasma CVD method.
₂ films are formed, and the SiO ₂ film is removed by photolithography and etching in the tapered region to be a stripe, and Ti / Pt / Au is used on the p-side and AuGe / Ni / Au is used on the n-side. A structure formed by forming an ohmic electrode can be used.

In the above structure, when a high frequency signal RF is applied from the driver 15 to the transducer 13a of the AOM 13, ultrasonic waves are generated in the ultrasonic medium 13b of the AOM 13,
It becomes a phase type diffraction grating to diffract the light beam 11. Then, the light beam 11 diffracted at the predetermined diffraction angle in the AOM 13 is emitted from the light beam 11 and then reflected by the mirror 14,
After returning to the original optical path, it is diffracted again at the AOM 13 and returned to the semiconductor optical amplifier 10 from its rear end face 10b. The emission wavelength of the semiconductor optical amplifier 10 depends on this self-injected light beam.
Locked to 11 wavelengths λ. The light 11F having the wavelength λ is amplified while traveling to the front side (right side in FIG. 1) in the semiconductor optical amplifier 10 and is emitted from the front end face 10c.

Next, the point of changing the emission wavelength λ will be described. As described above, the grating spacing of the diffraction grating is d, the predetermined diffraction angle in the AOM 13 is 90 ° -θ, and the AOM is
Assuming that the refractive index of the ultrasonic medium 13b of 13 is n, then λ = (2d sin θ) / n (θ and n are fixed). Therefore, the high frequency signal RF
If the lattice spacing d is changed by changing the frequency f of
The emission wavelength λ changes uniquely according to the value of.

In the present example, the semiconductor optical amplifier 10 having the above-described structure is originally capable of emitting light within a wavelength range of about 30 nm. On the other hand, the frequency f of the high frequency signal RF is, for example,
It is variable in the range of 75 MHz to 125 MHz, and accordingly, the lattice spacing d changes in the range of 3.4 × 10 ^{-5 to} 5.68 × 10 ^-5 m. Therefore, when θ = 1.2 ° and n = 2.26, the emission wavelength λ changes in the range of 630 to 1050 nm. The emission wavelength range is limited by the emission wavelength range of the semiconductor optical amplifier 10.

Unlike the mechanical driving, the frequency f of the high-frequency signal RF can be swept at a sufficiently high speed, so that the emission wavelength λ can be swept at a sufficiently high speed.

Further, this wavelength tunable semiconductor light emitting device is capable of sweeping the emission wavelength λ by electric operation and does not require any mechanical driving, and therefore has high reliability.

In the present invention, not only the so-called gain waveguide type semiconductor optical amplifier described above, but also a refractive index waveguide type semiconductor optical amplifier in which a refractive index step is formed between both side surfaces of the stripe and its outer portion. Can also be used. Further, as a semiconductor optical amplifier, for example, ELECTRONICS LETTERS (Electronic Letters) Vol. 19, (1982) p.169 and AP
It is also possible to use the phase-locked array type semiconductor optical amplifier shown in PLIED PHYSICS LETTER (Applied Physics Letter) Vol.60, (1992) p.668.

Further, although the bulk crystal type AOM 13 is used as the acousto-optic element in the above embodiment, the present invention is not limited to this, and an optical waveguide type acousto-optic element may be used.

[Brief description of drawings]

FIG. 1 is a schematic plan view of a wavelength tunable semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a schematic plan view showing an example of a conventional wavelength tunable semiconductor light emitting device having an external optical system.

[Explanation of symbols]

 10 Semiconductor Optical Amplifier 11 Optical Beam 12 Collimator Lens 13 AOM 14 Mirror 15 AOM Modulation Driver

Claims (1)

[Claims] 1. A semiconductor optical amplifier, and an acoustooptic device for diffracting light emitted from one end face of the semiconductor optical amplifier,
A wavelength tunable semiconductor light emitting device comprising a mirror for reflecting light diffracted at a predetermined diffraction angle by the acousto-optic element so as to return to the original optical path, and a driver for applying a frequency-variable high frequency signal to the acousto-optic element.